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.h

@@ -0,0 +1,42 @@
+#pragma once
+
+#include <m-string.h>
+
+/* Cli type
+ * Anonymous structure. Use cli_i.h if you need to go deeper.
+ */
+typedef struct Cli Cli;
+
+/* Cli callback function pointer.
+ * Implement this interface and use add_cli_command
+ * @param args - string with what was passed after command
+ * @param context - pointer to whatever you gave us on cli_add_command
+ */
+typedef void (*CliCallback)(string_t args, void* context);
+
+/* Add cli command
+ * Registers you command callback
+ * @param cli - pointer to cli instance
+ * @param name - command name
+ * @param callback - callback function
+ * @param context - pointer to whatever we need to pass to callback
+ */
+void cli_add_command(Cli* cli, const char* name, CliCallback callback, void* context);
+
+/* Read terminal input.
+ * Do it only from inside of callback.
+ * @param buffer - buffer pointer to char buffer
+ * @param size - size of buffer in bytes
+ */
+void cli_read(char* buffer, size_t size);
+
+/* Print to terminal
+ * Do it only from inside of callback.
+ * @param buffer - pointer to null terminated string to print.
+ */
+void cli_print(const char* buffer);
+
+/* New line 
+ * Send new ine sequence
+ */
+void cli_nl();