Refactor `__main__.main`.

[daankoning]

Especially the block for handling visualization speed (introduced in #6) is really hard to parse and requires weird exception handling.

brainfuck.py/src/brainfuckpy/__main__.py

Lines 32 to 45 in a3bb355

	evaluator = evaluate_brainfuck
	if "-vis" in sys.argv or "--visualize" in sys.argv:
	evaluator = visualize_evaluation
	try:
	if "-vrr" in sys.argv:
	speed_index = sys.argv.index("-vrr") + 1
	set_visualization_refresh_rate(float(sys.argv[speed_index]))
	elif "--visualization-refresh-rate" in sys.argv:
	speed_index = sys.argv.index("--visualization-refresh-rate") + 1
	set_visualization_refresh_rate(float(sys.argv[speed_index]))
	except ValueError:
	incorrect_usage()
	elif "-vrr" in sys.argv or "--visualization-refresh-rate" in sys.argv:
	incorrect_usage()

The other parts of this function are also quite ugly and unmaintainable, however. They should also get some attention. Most of them should simply be pulled into their own functions in order to keep main itself relatively clean.