Issue #2305

Require explicit turning on of history event merging.

Issue #2305

Issue #2321

Closes #2321

Slightly simplifies constructor logic.

Due to some elements still being stuck at the old height.

To account for the fact that the set of folded lines might be
different post-change and pre-change.

Issue #2305

Issue #2305

Conflicts:
	lib/codemirror.js
	package.json

Issue #2290

Closes #2200

Issue #2281

Issue #2283

Issue #2282

Closes #2278

Prevents focus loss in line widgets when they're updated.