Issue #121 Created Fork and Forks interfaces, RtForks class stub,
RtForksTest and RtForksITCase test classes.
Issue #121 Added Repo.forks() method, MkForks class stub and MkForksTest
unit test class.
Issue #121 Corrected NotNull message attribute for Forks#create()
Merge pull request #150 from carlosmiranda/121

#150: pull request Issue #121 Added Forks interface and Repo.forks() method