First batch of documentation refactoring.

Add:
	.doxygen.conf
		-add doxygen configuration file.

Mod:
	src/*.(c, h)
		-convert all existing comments to the Doxygen format, and add comments
		where they were lacking. Grant header files precedence in documentation
		over source files (ie, a function declared in a header file and defined
		in the corresponding source file will be documented in the header file).
Complete documentation refactoring.

Add:
	src/interpreter/shell*.(c, h)
		-complete project-wide conversion of existing documentation to the
		Doxygen format.
Minor documentation finalization and refactoring.

Add:
	src/screen.h
		-add overloaded varargs drawPixel() that allows the user to optionally
		specify the color of the pixel, as opposed to using the default
		TEST_COLOR.

	src/interpreter/shell.c
		-remove unnecessary usleep() from shell() main-loop, which is
		essentially accounted for by ncurses's getch() as it blocks on keyboard
		input.

Mod:
	src/**/*
		-replace multi-line comment end-delimiters "^*/$" with "^ */$", for
			consistency.