All gamepads I've come across work OK with button 2 or 3 as the primary
button, and button 1 or 4 as the secondary button. For the rest,
basically invariably, buttons 5 and 7 are the left shoulder buttons,
buttons 6 and 8 are the right shoulder buttons, button 9 is "Select"
or "Back", and button 10 is "Start". Based on this, I've changed
the gamepad controls to something that should work for most gamepads.
Also fixed some bad HTML in the documentation, and removed the
build instructions from there (they will soon be obsolete; I'm
working on replacing the hand-made Makefile with GNU Autoconf).