Also correct links to specification.

So that the addon doesn't try to put a single DOM node in two places

Closes #4848

Modern browsers handle updates to a textarea's value fast enough
to not do this anymore.

Issue #2703

Closes #4840

Issue #4839

Issue #4840

Closes #4839

Closes #4835

This way, only one char's left and right edges are used, instead of its
(logical) neighbour's right edges.

In bidi content, this avoids trying to scroll to two logically close,
but visually far apart positions in some situations.

Issue #4824

This reverts commit e7b737c8.

This prevents the test case search_expandingCaseFold from hanging in
Firefox 54 on Linux.

See https://discuss.codemirror.net/t/gfm-mode-doesnt-seem-to-respect-codeblock-mode-specific-indentation/1286

Issue #4819

into a form that CodeMirror can understand.

Ref: https://www.postgresql.org/docs/10/static/sql-keywords-appendix.html

Issue #4784

Issue #4787