* General code cleanup
* `NimBLEScan::start` will no longer clear cache or results if scanning is already in progress.
* `NimBLEScan::clearResults` will now reset the vector capacity to 0.
* `NimBLEScan::stop` will no longer call the `onScanEnd` callback as the caller should know its been stopped when this is called.
* `NimBLEScan::clearDuplicateCache` has been removed as it was problematic and only for the esp32. Stop and start the scanner for the same effect.
* `NimBLEScan::start` takes a new bool parameter `restart`, default `true`, that will restart an already in progress scan and clear the duplicate filter so all devices will be discovered again.
* Scan response data that is received without advertisement first will now create the device and send a callback.
* Added new method: `NimBLEAdvertisedDevice::isScannable()` that returns true if the device is scannable.
* Added default callbacks for `NimBLEScanCallbacks`
* `NimBLEScanCallbacks` function signatures updated:
* - `onDiscovered` now takes a `const NimBLEAdvertisedDevice*`
* - `onResult` now takes a `const NimBLEAdvertisedDevice*`
* - `onScanEnd` now takes a `const NimBLEScanResults&` and `int reason`
* Added new erase overload: `NimBLEScan::erase(const NimBLEAdvertisedDevice* device)`
* `NimBLEScanResults::getDevice` methods now return `const NimBLEAdvertisedDevice*`
* `NimBLEScanResults` iterators are now `const_iterator`
* Adds parameters `asyncConnect` and `exchangeMTU` to `NimBLEClient::connect`, default values work as the original connect method.
* * `asyncConnect`; if true, will send the connect command and return immediately with a true value for successfully sending the command, else false.
* * `exchangeMTU`; if true will send the exchange MTU command upon connection, otherwise not and the application can choose to do this later via the `exchangeMTU` method.
* Adds `onMTUChange` callback to `NimBLEClientCallbacks`
* Add `NimBLEDevice::getConnectedClients()` which returns a vector of pointers to the currently connected client instances.
* Calling `NimBLEClient::connect` will no longer cancel already in progress connections.
