Changed greyhounds markdown to an html page

Making this an html page lets me do more with the page, like add
some html specific stuff :-)
Added greyhounds page

This page is generated based on the data file in _data/greyhounds.yml
At the moment the page could look weird because I'm no doing anything
to change the size of the thumbnails
Merge pull request #1 from zachwhaley/master

Added greyhounds page