Added event support (except for storyboards)

[kszlim]

Added event support (breaks, videos, background)

I don't expect this to be accepted as is, but wanted to see if this is roughly along the lines of what you expect.

Missing: Docstrings Tests (1 simple test case is available)

[tybug]

not sure why I never reviewed this PR properly but I'll try and get this in once my exams are over (only 2 years late...)

[tybug]

I pushed some significant structure changes to try and get this into a better state. I also removed the unimplemented events (sprite/animation) instead of half-implementing them; was more trouble than it's worth. Let me know if you disagree with any of my changes.

[kszlim]

Honestly I've forgotten about how this PR mostly works, so feel free to make whatever changes you like.

[tybug]

no worries, I kinda figured that was the case

[tybug]

for anyone following along - I'm not happy with how this PR deals with not-yet-implemented events, so I need to work on that before pushing this along. I have some local changes to that effect but I'm not happy with them either. I would say it would be less effort to just fully implement the rest of the events, but storyboard events are so underdocumented that I don't really want to touch it yet.