USB VCP Cli (#237)

* Core: ring buffer.
* Api: usb vcp. F3: vcp glue code.
* Applications: cli draft version.
* Cli: basic working version, includes help and version commands
* HAL: vcp on f2
* Makefile: update openocd conf
* F3: vcp rx with freertos stream
* Cli: help
* Cli: standard commands, api-hal-uid
* Power: cli poweroff.

firmware/targets/f3/Src/main.c

@@ -111,6 +111,7 @@ int main(void)
   /* USER CODE BEGIN 2 */
   MX_FATFS_Init();
   delay_us_init_DWT();
+  api_hal_vcp_init();
   /* USER CODE END 2 */
 
   /* Init scheduler */