Built up more of the Window class. It's now even more in line with the
SDL2 code for SDL_Windows and SDL_Renderers.

Writer class now has function to return the maximum height (in pixels)
of a font. Also it's methods for setting and getting "pen color" have
been brought more in line with what was done in the Window class.

Major changes to the MainMenu state class. I'll let you figure out what
I did there :)