Gherkin support

Hacked into shape from this
https://github.com/cucumber/gherkin-syntax-highlighters
Ignore RubyMine cruft
Capture do, end, /^step def text$/
Gherkin test (I think)
Gherkin done
Step Defs

I think this is a bit simplistic, but it works
Add support for interactive ruby sessions (irb)
Add Nix language support
Nix: add class reference
fix Scala symbol literal
nix: fix example
nix: mark function parameters
Merge remote-tracking branch 'iElectric/nix'

Conflicts:
	docs/css-classes-reference.rst
Add x86asm syntax highlighter
SQL: Handle comments inside statements fixes #418
SQL: Updated author list
SQL: Added literals and built_ins
SQL: variablize comment mode
SQL: De-duplicate keywords, literals, and built-ins
Replace cyrillic 'и' by 'and' to avoid LaTeX error

Hi,

Currently there is a LaTeX error caused by a cyrillic letter in spec/text_spec.rb. I am proposing to replace it by its English translation 'and'.

Thanks.

Cédric