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.

applications/cli/cli_commands.h

@@ -0,0 +1,5 @@
+#pragma once
+
+#include "cli_i.h"
+
+void cli_commands_init(Cli* cli);