PySecure is now Python 3 Compatible

Changes to PySecure for Python 3 compatibility have now been checked in and pushed to PyPI.

A large amount of the labor went into refactoring nearly every occurrence of strings for string/bytes correctness. I also did an internal refactor of all of the tests (which largely just invoke a bunch of the functionalities and rely on the right exceptions to fail out when they should).

Unfortunately, I discovered that libssh’s reverse port-forwarding appears to be broken in 0.6.0 (which is incompatible with 0.5.5, for its authentication calls). This has been registered as bug #126 in their tracker.