Fix crash in contentEditable input style when editing near a bookmark.
Make sure change origins are preserved when splitting changes on read-only marks.
d mode: Support nested comments.
python mode: Improve tokenizing of operators.
markdown mode: Further improve CommonMark conformance.
css mode: Don’t run comment tokens through the mode’s state machine.
shell mode: Allow strings to span lines.
search addon: Fix crash in persistent search when
extraKeys is null.