Make keyword lexing actually work.

Keyword lexing intentionally eats dots to prevent detecting keywords in attribute names accessed through dots. This wasn't working because of the extra `\` in the lexeme regexp and a dot starting rvalue containers.
Zeroed relevance of E4X in JavaScript.
Reset relevance of Perl subst to 1.
More relevance work:

- Illegalized `<` and `>` in the top mode of SQL.
- Reset XML tag relevance to 1 (was: 0).
"this" is not a PHP keyword.
Merge branch 'master' of github.com:isagalaev/highlight.js