- highlight strings
- highlight ports as numbers in expose instruction
- highlight comments as such only when they appear at the start of a line
- consider also ` as a line continuation

Turn it off for mssql

Closes #5229

[asynchronous
iteration](http://2ality.com/2016/10/asynchronous-iteration.html) is a
stage 4 ("finished") feature in ES2018, and its additional syntax - for
await loops - don't require too much change in CodeMirror's JavaScript
mode for support.

[javascript-lint] JSHINT backward compatibility - Setting error severity to error by default when there is no error.code property (#5260)

Closes #5256

CodeMirror C and C++ currently highlight the string "null", which isn't defined in C/C++. Those languages do macro "NULL", though.

Closes #5248

add more instructions
highlight instructions as 'keyword'
highlight 'from ... as'
add tests

Closes #5238

In my experience, `.tex` is a much more common extension for LaTeX documents.

In addCursorToSelection, keep the cursor's position after short lines.

Closes #5221

Closes #5219

Closes #5217

Closes #5197

When using tabs for indentation, the markers would not always align with the actual problem.
The old workaround for JSHint never really worked (only when a line had one tab) and I found a simple option which fixes the issue.
This time I also checked backwards compatibility, which works even fine with the old JSHint version R07.
As a second marker fix, I added an error line check, since JSHint for some reason adds configuration issues in the errors array with line: 0, character: 0. Now, if you pass an invalid option you will get a console error instead of an invisible marker.

As of 1d5c828f the missing js semicolon is a warning and not an error anymore, therefore I added an error elsewhere.