Add Lua API twrite

The twrite Lua API is a variation of the write API, with the output
character mapping and output-delay / output-line-delay features enabled.
Since it processes each character internally, writing speed is slower
than the write API.

~~~~~~~~~~~~~~~~~~~~~~~
twrite(string)
    Translate string with output character mapping and write the
    translated string to serial device with output-delay /
    output-line-delay.

src/tty.h

@@ -84,3 +84,5 @@ void tty_input_thread_wait_ready(void);
 void tty_line_set(int fd, tty_line_config_t line_config[]);
 void tty_search(void);
 GList *tty_search_for_serial_devices(void);
+void forward_to_tty(int fd, char output_char);
+void tty_sync(int fd);