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

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

Closes #2200

Added a wrapper for js-yaml.js to enable YAML lint support. Followed
json-lint.js pattern. Unfortunately js-yaml.js only shows one error at
a time, but something is better nothing. Checked code with linter and
ran tests. All came back clean.

Issue #2253

add docs that when completions are object they can have a from: and to:
that will be used by pick.

Make sidebar in manual scrollable for small screen especially usefull
when `Programming API` is unfolded

seem to look nice on Chrome and Firefox Osx, (scrollbar do not appear,
except when scrolling on Chrome) but should maybe be tested on linux.

Add //-comment support for F#

Issue #2136

Issue #2107

Closes #2059

Add getHelpers and registerGlobalHelper, allow modes to specify arrays
of helper names, support modeProps in mode specifications.

Update foldcode and show-hint to make use of more powerful helper
system by defining an `auto` helper that tries multiple helpers, and
using that as default.

And update Light Table link

Stop doing this automatically for marks inclusive on both
sides.

Issue #1996

HTML5 tag parsing hack, and invert css media query.

Issue #649