TODO

   1 Finish rules translation in Spanish + improve existing ones
   2 Design: final touch (gain extra space on top, using space on the right)
   3 Crazyhouse: center reserves, grey if zero available, numbers superimposed
   4 Promotions: increase pieces sizes, better background.
   5 Code: use two spaces instead of tabs, everywhere.
   6 Increase code line length to 100 or more?
   7 (http://katafrakt.me/2017/09/16/80-characters-line-length-limit/)