Use gitlab.com repo

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'master' into 'master'

Use GitLab.com test repo

See merge request !9
Make Commit and Diff objects wrap Rugged objects

Allow a Gitlab::Git::Commit or a Gitlab::Git::Diff object to be created
from either a Rugged or a Grit object.
Implement the log() method with Rugged

Use Rugged's Walker API to implement the log() method instead of using
Grit.
Fix coding style

Fix coding style issues from houndci.
Implement the 'follow' option in Repository.log()

Implement the 'follow' option for the log() method, and add tests.
Fix coding style
Implement Repository.submodules() with Rugged

Replace Grit with Rugged in the submodules() method.  Rugged doesn't
have any submodule functionality in its API, so just read the
.gitmodules file directly.
Remove Grit from the Commit class
Replace Grit in Repository

Implement more methods in the Repository class with Rugged instead of
Grit.