Added file parameter, fixed functionality, and changed spacing.

Fixed regex because GitHub gists have hexadecimal IDs
now, not numeric.

Changed spacing to tabs in accordance with MediaWiki
coding standards. Also added file and files parameters
to allow specification of one or multiple files.

Fixes: #1
General cleanup and optimization.

Fixed documentation and other spacing. Made files logic
simpler and used empty() instead of isset() in case of
no files specified. Also replaced preg_match with ctype_xdigit
and the manual script tag with Html::linkedScript.
Merge pull request #2 from Parent5446/cleanup

Cleanup and add file parameters.