regexp: add jsSpecial to jsRegexpSpecial cluster

Most significantly, this causes shorthand character classes within
groups to be highlighted. For example:

    /(\d)/
limit scope in which jsSpecial may be matched
Merge pull request #169 from davidchambers/shorthand-character-classes

regexp: add jsSpecial to jsRegexpSpecial cluster
Adding additional `contained`s

The intention of this commit is to perhaps improve performance, but also
clean up a bit of the how a couple regexes are used.

By adding `contained` to `jsObjectKey`, I think we might get a nice
performance boost, especially on larger files since it won't attemp that
lookbehind everywhere.

Adding `contained` to the newer regex for string templating stuff
in ES6 seems more 'accurate' or proper.
Merge pull request #170 from pangloss/add-misc-contained

Adding additional `contained`s
highlight "use strict"; as PreProc

This is part of the ECMAScript 5 standard, so I think it makes sense to
highlight it as a preprocessor command.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions_and_function_scope/Strict_mode

Updated to use backreference as suggested by @davidchambers