Use website url for Vimeo videos.

Vimeo video pages have a swf for the `og:video` meta tag, which cannot be parsed by VideoInfo into something meaningful.

Switching to `og:url` specifically for Vimeo pages fixes this (the video metadata returned is now far more detailed).
Document Vimeo workaround in code.
Merge pull request #46 from mhaylock/better_vimeo_detail

Use website url for Vimeo videos