add "share" button for search results

"share" button appears on search results; clicking pops up a markdown version of the search result with a link to that search result (on your current page).

![Screen Shot 2013-04-12 at 8 49 57 PM](https://f.cloud.github.com/assets/455632/375926/9769ec8a-a3dc-11e2-8386-21bdc8bfba25.png)
![Screen Shot 2013-04-12 at 8 50 07 PM](https://f.cloud.github.com/assets/455632/375927/976fa530-a3dc-11e2-9c55-2ba740be42fa.png)