[closetag addon] Work better with htmlmixed mode

It now closes script and style tags when the slash is typed

Closes #2797
[javascript mode] Fix parsing of argument-less fat arrow functions

Closes #2794
[smalltalk mode] Use \s instead of space in regexps that denote whitespace

Closes #2796
Add a requireJS demo
Improve isWordChar() for Arabic language
Fix handling of electricChars in multi-line edits

Closes #2804
Make parentheses visible while under `matchingbracket` rule

Code: Brackets now become black when they are highlighted as "matching".
JSON: key names are now in "white" (json was a bit saturated with orange - keys and string values).
Cleanup: removed some unnecessary rules.
Default face color normalized to #ffffec (was #ffffe9).
[show-hint addon] Give active hint color more precedence

To make it easy for client code to color completions without clashing
with the selected styling.
Update shell.js
Added wordsOnly option. Updated documentation.
Add example of using markselection to style background to demo
Add links to addon docs in mark-selection demo
Support upper-case SCRIPT tags in htmlmixed mode
[xml mode] Mark <menuitem> as self-closing tag

Closes #2810
[rst mode] Remove assertion mechanism

Throwing exceptions is a really bad way to deal with unexpected
syntax in a highlighting mode.

Closes #2805
Update realworld.html

Added hawkee.com
Mark release 4.6
Bump version number post-4.6
[markdown mode] test case for #2813

after header immediately followed by a code block, GFM formatting is
broken (SHA, #issue, URLs).

overlay.codeBlock gets it wrong (false inside fenced block, true after).
Not yet sure why.
[markdown] Fix handling of forced blank lines (after headers)

Closes #2813