Some more meta-changes.
Almost finished with delta-based plugins, but the deltas do not yet have 'side effects'. They only return a new object based on the old object.
Fully implemented delta-based plugins, added 3D support detection, and fixed the bug where tile-clicking and 3D-dragging didn't interact.
Removed 3D support detection cache (just test it every time).
Made `compose` side-effecty, like `apply`.
Fixes #7. Fixes #8. Plugins based on deltas are now finished, and every plugin is rewritten to the nicer API.