Update screenshot to include commit links.
Minor improvement to favicon handling.

This catches both /favicon.ico and /favicon.ico/ queries.
Use own vcsstore instance since Sourcegraph's is not accessible at this time.

As described in #23.
Add support for golang.org/x/... packages (displaying their changes).

Use underlying vcs type and remote url instead of import path for vcs
operations.
This should enable support for non-Mercurial repos hosted on
code.google.com (they are rare, but do exist).