Add MiniSTM32 BSP, which is created 2 years ago. Now it needs to be modified to fit new version of RTT.
[miniStm32] Fix "core_cm3.c" compile error
[miniStm32]
1. Fix USART driver bugs
2. Modify SPI driver as USART driver
3. Fix a define in "board.h", which conflicts with a define in new version of RTT