Closes #4548

Issue #4485

Issue #4413

Adds an option to keep the active line highlighted even when text
inside the line is selected.

This reverts commit 8a1dd160.

Issue #4123

Issue #4217

Closes #4172

Since the only pre-build version of csslint was changed to some
global-scope-polluting mess that breaks our module loader headers.

Issue #4123

Issue #3974

Even if we don't use promise internally, check for the existence of
`.then` attributes on the return results of a hinting function, and if
so assume it is a promise.

Internally also convert all hinters to use the asynchronous interface
for consistency and simplification of code paths.

Closes #3971

Closes #3791

When enabled, and the annotatescrollbar addon is loaded, matches will
be shown on the scrollbar.

Issue #3682

Closes #3569

Issue #3586

Issue #3548

Fixes #3449

Issue #3423

... and export (via defineExtension) a method to explicitly trigger
linting from user code.

Issue #3337
Issue #3338

Spent quite a while perfecting this (IMO), but a lot of people seem to
really like it. Hope you do too.

Issue #3320

https://github.com/codemirror/CodeMirror/pull/3212

Closes #3159