Show preview of the gorgeous gif when hovering over link

This change improves selecting the right gif by 238%. When hovering with
le mouse over a link, it shows the corresponding gif in the sidebar.
Merge pull request #16 from pangratz/add_preview

Show preview of the gorgeous gif when hovering over link
update site index
Addresses #16: replace top left corner img with preview img
change href to absolute link for other domain
change to relative url for joelglovier.com/gifs