Reduce huge jumbotron bottom margin to something more consistent.
Merge pull request #236 from ellisonbg/jumbo-margin

Reduce huge jumbotron bottom margin to something more consistent.
fix front page link to IPython docs
update link to R magic extensin
Merge pull request #237 from Carreau/update-R-link

update link to R magic extension
Adding new user and user/repo shortcutst to Go form.
Starting to improve the shortcuts docs.
Main page layout and shortcut table.