* Exchange map for vector, saving 1,076 bytes of program memory and 5,024 bytes of heap for a small device (LYWSD03MMC)
* Removing m_characteristicMapByHandle (using the handles form m_characteristicVector instead) saving in total (compared to the current master) 1,508 bytes of program memory and 6,500 bytes of heap for a small device (LYWSD03MMC)
* Change NimBLEScan container from std::map to std::vector
* Add function to get advertised device by address
* Update documentation
Previously we used createServer() to get a reference to the server instance.
This was problematic when using advertising only as it would create a server
when starting advertising. This prevents that and provides better semantics.
This allows NimBLE options in menuconfig to reduce code size based on
the roles selected (scan/advertising/central/peripheral).
Significant code space can be saved by removing unnecessary roles for the application.
