Custom obtvse overrides for Gist styling

Custom obtvse overrides for Gist styling:
- hide the default gist line numbers and implement css-counter
  based line numbering, accommodating word wraps and perfect fit between
  numbers and lines
- line-height and font-size modified for better presentation of code;
  previously they inherited obtvse styling for post text and presentation
Merge pull request #111 from tarakanbg/master

Custom obtvse overrides for default Gist styling