Add examples & Github Actions test for ESP-IDF.

This pull request adds two examples and tests using the ESP-IDF framework:

* A test with the Arduino GFX library (which requires the arduino-esp32 library & Arduino BusIO library)
* A test without the Arduino GFX library, which can be compiled without any additional dependencies.

Having these tests helps prevent any future regressions that may break users of the ESP-IDF platform.

.github/workflows/esp-idf_with-gfx.yml

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+name: esp-idf with Adafruit GFX Library
+
+on:
+  push:
+    paths-ignore:
+      - '**.md'
+      - 'doc/**'
+      - '.github/**'
+  pull_request:
+    paths-ignore:
+      - '**.md'
+      - 'doc/**'
+      - '.github/**'
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout repo
+      uses: actions/checkout@v2
+      with:
+        submodules: 'recursive'
+    - name: Checkout ESP32-HUB75-MatrixPanel-I2S-DMA component
+      uses: actions/checkout@v2
+      with:
+        path: 'examples/esp-idf/with-gfx/components/ESP32-HUB75-MatrixPanel-I2S-DMA'
+    - name: Checkout Adafruit-GFX-Library repo
+      uses: actions/checkout@v2
+      with:
+        repository: 'adafruit/Adafruit-GFX-Library'
+        path: 'examples/esp-idf/with-gfx/components/Adafruit-GFX-Library'
+    - name: Checkout Adafruit_BusIO repo
+      uses: actions/checkout@v2
+      with:
+        repository: 'adafruit/Adafruit_BusIO'
+        path: 'examples/esp-idf/with-gfx/components/Adafruit_BusIO'
+    - name: Checkout arduino-esp32 repo
+      uses: actions/checkout@v2
+      with:
+        repository: 'espressif/arduino-esp32'
+        path: 'examples/esp-idf/with-gfx/components/arduino'
+    - name: esp-idf build
+      uses: espressif/esp-idf-ci-action@v1
+      with:
+        esp_idf_version: v4.4.4
+        target: esp32
+        path: 'examples/esp-idf/with-gfx'

.github/workflows/esp-idf_without-gfx.yml

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+name: esp-idf without Adafruit GFX Library
+
+on:
+  push:
+    paths-ignore:
+      - '**.md'
+      - 'doc/**'
+      - '.github/**'
+  pull_request:
+    paths-ignore:
+      - '**.md'
+      - 'doc/**'
+      - '.github/**'
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout repo
+      uses: actions/checkout@v2
+      with:
+        submodules: 'recursive'
+    - name: Checkout ESP32-HUB75-MatrixPanel-I2S-DMA component
+      uses: actions/checkout@v2
+      with:
+        path: 'examples/esp-idf/without-gfx/components/ESP32-HUB75-MatrixPanel-I2S-DMA'
+    - name: esp-idf build
+      uses: espressif/esp-idf-ci-action@v1
+      with:
+        esp_idf_version: v4.4
+        target: esp32
+        path: 'examples/esp-idf/without-gfx'

examples/esp-idf/.gitignore

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+# ESP-IDF default build directory
+build
+
+# Temporary files
+*.swp
+
+# lock files for examples and components
+dependencies.lock
+
+sdkconfig*
+# Unignore sdkconfig.defaults
+!sdkconfig.defaults

examples/esp-idf/with-gfx/CMakeLists.txt

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+# This is a boilerplate top-level project CMakeLists.txt file.
+# This is the primary file which CMake uses to learn how to build the project.
+#
+# Most of the important stuff happens in the 'main' directory.
+#
+# See https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/build-system.html#example-project for more details.
+cmake_minimum_required(VERSION 3.5)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(with-gfx)

examples/esp-idf/with-gfx/README.md

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+# ESP-IDF Example With Adafruit GFX Library
+
+This folder contains example code for using this library with `esp-idf` and the [Adafruit GFX library](https://github.com/adafruit/Adafruit-GFX-Library).
+
+First, follow the [Getting Started Guide for ESP-IDF](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/get-started/index.html) to install ESP-IDF onto your computer.
+
+When you are ready to start your first project with this library, follow folow these steps:
+
+  1. Copy the files in this folder (and sub folders) into a new directory for your project.
+  1. Clone the required repositories:
+     ```
+     git clone https://github.com/mrfaptastic/ESP32-HUB75-MatrixPanel-DMA.git components/ESP32-HUB75-MatrixPanel-I2S-DMA
+     git clone https://github.com/adafruit/Adafruit-GFX-Library.git components/Adafruit-GFX-Library
+     git clone https://github.com/adafruit/Adafruit_BusIO.git components/Adafruit_BusIO
+     git clone https://github.com/espressif/arduino-esp32.git components/arduino
+     ```
+  1. Build your project: `idf.py build`

examples/esp-idf/with-gfx/components/.gitignore

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+# Ignore everything in this directory
+*
+# Except this file
+!.gitignore

examples/esp-idf/with-gfx/main/CMakeLists.txt

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+idf_component_register(
+			SRC_DIRS "." ${SRCDIRS}
+			INCLUDE_DIRS ${INCLUDEDIRS}
+			REQUIRES ESP32-HUB75-MatrixPanel-I2S-DMA
+                       )

examples/esp-idf/with-gfx/main/main.cpp

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+#include "ESP32-HUB75-MatrixPanel-I2S-DMA.h"
+
+MatrixPanel_I2S_DMA *dma_display = nullptr;
+
+extern "C" void app_main() {
+  HUB75_I2S_CFG mxconfig(/* width = */ 64, /* height = */ 64, /* chain = */ 1);
+
+  dma_display = new MatrixPanel_I2S_DMA(mxconfig);
+  dma_display->begin();
+  dma_display->setBrightness8(80);
+  dma_display->clearScreen();
+  // `println` is only available when the Adafruit GFX library is used.
+  dma_display->println("Test message");
+}

examples/esp-idf/with-gfx/sdkconfig.defaults

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+CONFIG_FREERTOS_HZ=1000

examples/esp-idf/without-gfx/CMakeLists.txt

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+# This is a boilerplate top-level project CMakeLists.txt file.
+# This is the primary file which CMake uses to learn how to build the project.
+#
+# Most of the important stuff happens in the 'main' directory.
+#
+# See https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/build-system.html#example-project for more details.
+cmake_minimum_required(VERSION 3.5)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(without-gfx)

examples/esp-idf/without-gfx/README.md

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+# ESP-IDF Example Without Adafruit GFX Library
+
+This folder contains example code for using this library with `esp-idf`.
+
+First, follow the [Getting Started Guide for ESP-IDF](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/get-started/index.html) to install ESP-IDF onto your computer.
+
+When you are ready to start your first project with this library, follow folow these steps:
+
+  1. Copy the files in this folder (and sub folders) into a new directory for your project.
+  1. Clone the required repositories:
+     ```
+     git clone https://github.com/mrfaptastic/ESP32-HUB75-MatrixPanel-DMA.git components/ESP32-HUB75-MatrixPanel-I2S-DMA
+     ```
+  1. Build your project: `idf.py build`

examples/esp-idf/without-gfx/components/.gitignore

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+# Ignore everything in this directory
+*
+# Except this file
+!.gitignore

examples/esp-idf/without-gfx/main/CMakeLists.txt

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+idf_component_register(
+			SRC_DIRS "." ${SRCDIRS}
+			INCLUDE_DIRS ${INCLUDEDIRS}
+			REQUIRES ESP32-HUB75-MatrixPanel-I2S-DMA
+                       )

examples/esp-idf/without-gfx/main/main.cpp

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+#include "ESP32-HUB75-MatrixPanel-I2S-DMA.h"
+
+MatrixPanel_I2S_DMA *dma_display = nullptr;
+
+extern "C" void app_main() {
+  HUB75_I2S_CFG mxconfig(/* width = */ 64, /* height = */ 64, /* chain = */ 1);
+
+  dma_display = new MatrixPanel_I2S_DMA(mxconfig);
+  dma_display->begin();
+  dma_display->setBrightness8(80);
+  dma_display->clearScreen();
+}

examples/esp-idf/without-gfx/sdkconfig.defaults

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+CONFIG_ESP32_HUB75_USE_GFX=n