yaml->json initial attempt
add json characters file
add entities.json, improve characters.json
remove yaml entirely from cmake, parser works beautifully now

it's also way more competent and robust at error handlig than the
yaml stuff ever was...i was able to check at many points where invalid
input can happen/malformed data, and spit out appropriate error message
Merge branch 'jsonify' into custom-physics

Conflicts:
	src/spritesheetparser.cpp