Issue #2305

Conflicts:
	lib/codemirror.js

Issue #2305

Issue #2305

It causes noticeable missinge scrollbar in some cases.

Closes #2317

pressing Ctrl-Space once starts the selection extension mode,
pressing it again cancels that

It was broken and confused.

Make the mode register a list of completable words instead.

Issue #2324

Since it's what you want most of the time, and easy to forget.

Issue #2305

Issue #2332

In Vim, defaults keymap cannot be unmapped. They must be explicityly
set to <NOP>. In this case we allow that because
user defined maps are stored in the same map as the defaults.

Closes #2331

If a line has widgets with heights, use them when estimating line height.

This prevents a .refresh() call from reverting to less accurate line
heights.

Issue #2305

Issue #2323

Require explicit turning on of history event merging.

Issue #2305

Issue #2321

Closes #2321

And listen for them in the merge addon.

Per change authored in https://github.com/marijnh/CodeMirror/pull/1979.

Closes #2309