Add option 'clearOnEnter' to foldcode.js and default it to true.
This option determines whether the marker added when folding a
line clears when the cursor enters it.

Closes #4042

See https://discuss.codemirror.net/t/width-of-sql-hint-dropdown-in-firefox-is-not-always-correct/757

It breaks document tree rebalancing.

Closes #4032

See https://discuss.codemirror.net/t/dynamically-switch-mode-with-sql-hint-addon-bugs/751

Closes #3796

Closes #3896

Closes #3900

Issue #3983

Closes #4030
Closes #4031

Closes #3926
Closes #4026

To make it clearer that they are updated together

Issue #4028

Closes #3983

Closes #745

This reverts commit 8dbb84f4.

Issue #3127

Add gutters properties (grid-gap, grid-column-gap and grid-row-gap):
https://www.w3.org/TR/css-grid-1/#gutters

Take advantage to add some missing keywors:
* grid and inline-grid: https://www.w3.org/TR/css-grid-1/#grid-containers
* dense: https://www.w3.org/TR/css-grid-1/#grid-auto-flow-property

It's been a while since the list of properties has been updated:
https://drafts.csswg.org/css-grid/#property-index

1. Mention multiplex as a dependency
2. Add ERB as a MIME-type

Closes #4025

Issue #2901

Issue #4022

Closes #4020

Closes #4012

Closes #4009

Issue #4013

Closes #4013

Closes #3998