Fix various API doc issues and typos

Partially based on an old patch by Adrian-Ken Rueegsegger.

src/charon-cmd/charon-cmd.c

@@ -150,7 +150,7 @@ static int run()
 				return 0;
 			}
 			case SIGUSR1:
-			{	/* an error occured */
+			{	/* an error occurred */
 				charon->bus->alert(charon->bus, ALERT_SHUTDOWN_SIGNAL, sig);
 				return 1;
 			}

src/charon-cmd/cmd/cmd_connection.h

@@ -14,6 +14,11 @@
  */
 
 /**
+ * @defgroup charon-cmd charon-cmd
+ *
+ * @defgroup cmd cmd
+ * @ingroup charon-cmd
+ *
  * @defgroup cmd_connection cmd_connection
  * @{ @ingroup cmd
  */