add tests and documentation for clone feature
fix tests

Now, we verify only some references in cloned repository. Looks like output of
git show-ref --heads --tags is different from a version of git to another
Unset the HOME env before calling git binary

If we do no unset the env, git will use a potential
.gitconfig which can alter results
Cleaned some code
Added support for Commit::getSubjectMessage and Commit::getBodyMessage
Fixed Commit::getShortMessage

Do not cache result since the method took arguments
Added support for remote branches
Added support for Commit::getIncludingBranches