Board support for STM8L152 (nucleo board)

[JirkaKrivanek98]

Please add support for the STM8L152R8 (nucleo board/bare metal).

Official toolchain is pretty old and is not well maintained. Alternative through ArduinoIDE is better but pretty limited (timers, ports manipulation, etc...). IC's are cheap, available, and more powerful then Arduino UNO.

[maxgerhardt]

For STM8 bopards, please file an issue in https://github.com/platformio/platform-ststm8/issues