Allows partial matching on latest-features

Before this was relying on pattern for git for-each-ref however
it only allowed matching branch names between slashes.

Eg.: refs/remotes/origin/foo-branch/

-p foo # no match
-p foo-branch # matches

This now keeps the same API as before (-p pattern) but allows partial
matching so -p foo and -f foo-branch both yield the same results for
the same scenario

This closes #24
Merge pull request #26 from mezis/fix-issue-24

Allows partial matching on latest-features