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/Inc/api-hal-vcp.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+
+/* Init VCP HAL
+ * Allocates ring buffer and initializes state
+ */
+void api_hal_vcp_init();
+
+/* Recieve data from VCP
+ * Waits till some data arrives, never returns 0
+ * @param buffer - pointer to buffer
+ * @param size - buffer size
+ * @return items copied in buffer, 0 if channel closed
+ */
+size_t api_hal_vcp_rx(uint8_t* buffer, size_t size);
+
+/* Transmit data to VCP
+ * @param buffer - pointer to buffer
+ * @param size - buffer size
+ */
+void api_hal_vcp_tx(uint8_t* buffer, size_t size);