Add mnimalistic command line interface "command.c"

This is a very simplistic command line interface parser which
various parts of the code can use to register textual commands
on the debug UART.

Change-Id: I2d289228fb97ecde5602e9756f3d7c51fa65a3b7
diff --git a/sysmoOCTSIM/command.h b/sysmoOCTSIM/command.h
new file mode 100644
index 0000000..cdf256d
--- /dev/null
+++ b/sysmoOCTSIM/command.h
@@ -0,0 +1,20 @@
+#pragma once
+
+struct command_fn {
+	const char *command;
+	const char *help;
+	void (*fn)(int argc, char **argv);
+};
+
+#define DEFUN(funcname, cmdname, cmdstr, helpstr)	\
+	static void funcname(int argc, char **argv);		\
+	static struct command_fn cmdname = { 			\
+		.command = cmdstr,				\
+		.help = helpstr,				\
+		.fn = funcname,					\
+	};							\
+	static void funcname(int argc, char **argv)
+
+void command_init(const char *prompt);
+int command_register(const struct command_fn *cmd);
+void command_try_recv(void);