Milestone commit. The program is pretty much built, at least for the
two-player mode. This commit is for some touch-ups such as comments and
style changes. Also, all header files have been changed to the extension
".hpp", because I am slightly OCD like that.

Remaining work includes making the GUI actually pretty, i.e. aligning
stuff and defining sizes. Also, the computer player AI must be coded,
and thus I am working on a Negamax implementation as a seperate project.