Add screen-saving, rm engine.h, add to gitignore.

Add:
	src/screen.c
		-add writeScreen(), which writes the current SDL_Surface to a file.

	src/parser.c
		-add documentation comments before every function header
		-add ability to save current SDL screen to file from a script.

	src/(engine, globals).h
		-move the only declarations in engine.h, MAP_HEIGHT and MAP_WIDTH
		macros, to the globals header, and remove engine.h (engine.h was being
		used as a globals file, which is better conveyed by a file called
		globals.h).

	.gitignore
		-add *.bmp files