Octopress 2.1 Line Markup Compatibility and more 'found on' code

1. Allows the line markup options added to Octopress in 2.1 to be used in Foxslide- this code was pulled direct from the Octopress 2.1 classic theme.
2. Adds additional 'found on' options for:

    * Vimeo
    * 500px
    * Steam
    * 360cities.net

Changes should be backwards compatible with Octopress 2.0, as the added markup code is just not referenced (I think? I muddle my way through CSS), but neither this nor compatibility with the develop branch of Octopress was tested.

Figured you might want this code hanging around for reference when a new Octopress is released.