XBoard Enhancement and Accessibility

Finally I just committed the KeyNavigation patch to branch named "gtk3".

http://git.savannah.gnu.org/cgit/xboard.git/commit/?h=gtk3&id=200fb1b09fa0eb68d877f0f58cf89c876dc43d05

Now we have a menu named "Accessibility" which contains functions to announce information about the board.

Currently we use espeak to announce these information instead of passing to orca screen reader. Yes we do this to start testing in parallel.