Initial Working Implentation

- Wrote GUI code and a main module that connects the board logic with
the gui display.  Running main.py will now run a working version of the
application.  However, this implementation makes use of a global
variable (the game board data representation) and dynamically injects
functions into an instantiated App object, which is suboptimal.
Refactoring required, most likely by pulling out the Tkinter eventloop
and the scheduling of ticks from the gui code to the main module.

- README also updated to describe the game in more detail.