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/api-hal/api-hal-uuid.c

@@ -0,0 +1,10 @@
+#include <api-hal-uid.h>
+#include <stm32wbxx.h>
+
+size_t api_hal_uid_size() {
+    return 64/8;
+}
+
+const uint8_t* api_hal_uid() {
+    return (const uint8_t *)UID64_BASE;
+}