Code cleanup

-) `th_new_input()` is now the main thread, since signals
    will be caught from readline
-) structure `dchat_conf_t`: removed `userin_th` and added
   `select_th` instead
-) added ansi escape code functions to utilise colours
-) colorised prompt and text messages
-) changed names of long options
-) adapted names of long options in the man page
-) adapted usage() to use the new long option names
-) updated TODO and NEWS