tws:
* added 'twat' to swear list
* added word limit to settings
* refactored call_main
* main and bonus word lists are now sorted alphabetically instead of
  shuffled, thus sfyshuffle() was removed
* made some style adjustments to index.html to make it slightly more
  usable in mobile. It's still designed for a desktop browser but you
  can read the labels now.

other:
* added reverse lookup and swear listing/searching to find_word.c
* added build targets to Makefile