Start to replace Grit
Move `ref_to_sha!` to rugged
Move GitAccess#tree to Rugged
Move GitAccess#commit to rugged
Move BlobEntry#blob to rugged
update documentation
Populate pages with the whole blob_entry

Not just the blob, because i don't think i can get the name from
the Rugged::Blob.
Rescue Rugged stuff instead of Grit
Start using Rugged::Commit to get show something

At this point, running Gollum on this repo will show the Home, readme,
and history pages, but don't try doing too much else...