modules/uart.c: The classic adage - return pmod_error(...);
stm32/lua_lcd.c: Add support for PicoC.
stm32/enc.c: Add support for PicoC.
stm32/conf.py: Change lib order.

* Also check lm3s/conf.py
stm32/platform.c: Add preliminary support for PicoC.
stm32/platform_conf.h: Add preliminary support for PicoC.
Add platform_picoc.h for the stm32 target.