Use git-log instead of git-blame-tree

This relies on a standard git command to reduce special dependencies.
Enable nice debugging output in debug mode
Use more robust detection of debug mode
Fix searches
Add word diffs in commit views

This shows changes between adjacent lines rather than just showing the
lines have changed.
Make goblet work in URL subpaths

It is not possible to run it as e.g. http://example.com/goblet/ instead
of needing it to be installed at the URL root.
Always use matching scheme to access fonts

If goblet is accessed over SSL, fetching fonts without SSL triggers an
SSL warning.
Always use flask.sendfile for cache files

Exposing repository files directly seems problematic. This will still
use X-Sendfile when enabled to allow good speed.