Added a get_blob method to Repository
Added a view to serve blobs, and one to serve blob images

Images are hard. BlobDetail's template can look at its context to see
if a blob is an image, and then link to ImageBlobDetail to get the
image.
Created a view for BlobDetail
Added a couple of functions to inspect blobs.

One determines if it's a binary based on the file's contents, the
other checks to see if it's an image based on its filename
Fixed a security issue for the commit_message filter

If commit messages contained any javascript, it would have been
executed... now that stuff's being escaped.
Added a filter to run pygments on code
Updated commit detail page to use safer commit_message filter
Added links to blobs
Added urls to blob views
Merge branch 'feature/blob' into develop