Better diff for file-moves

Repro steps

1. Commit a file with some contents
2. Rename the file
3. Make a tiny change to the file's contents
4. Commit those changes
5. Look at the commit in Bitbucket

Expected

Bitbucket should tell me that the file was renamed, and highlight the salient changes.

Actual

Bitbucket says one file was deleted, and another was added. Bitbucket does nothing to show you the relationship between them.