Bash: Change style of the IA.

- Put query in the header.
- Change <code> to <pre>
- Add CSS file to change the look of the <pre> tag.
Bash: Update tests.
Bash: Encode the heading.
Bash: Change regexp to make it work with a different format.

We need to accept `if [ ! "something" -gt "150" ] bash` too.
Bash: Split the regexp to make it clearer.

Thanks to @kablamo for pointing that out.
Bash: Stricter regexp for arguments.

Don't just use `/.+/` for accepting arguments. We need to prevent nested `[[]]`s and a few invalid forms.
Bash: Add an introduction at the beginning.
Bash: Start with "The Bash expression ..."
Merge pull request #374 from duckduckgo/jag/bash

Bash: Ready for release!