JSON-ify the credits

This commit makes the credits proper JSON, which is fun :) Unfortunately
I also realized that drawing the credits in top-down order causes the
curly brackets to get truncated, and broke the gradual display in the
process of trying to fix that. Will fix in later commit (or Alex will)
Merge branch 'bossFight' of github.com:AlexNisnevich/untrusted into bossFight

Conflicts:
	levels/XX_credits.jsx