Patches and extensions to unittest

[mMerlin]

This is a collection of small updates I added to my own copy of unittest.py to handle missing and broken cases noticed while using it.

• handle and report exception running test method that occurs outside of assertraises
• allow running testmodules from a sub folder instead of only in the root
• add a tests folder and duplicate example unit test to demonstrate subfolder usage
• skip looking for tests earlier if TestCase shows up in a module search (versus subclass)
• properly pass skip reason message to raised exception
• add new options for running to the README
• add whitespace to the readme markdown to make the linter happy
• move TestResults class before first reference in the module
• implement bare (do nothing) hooks in the TestCase base class
• move core test method run loop from run_class to TestCase.run
• rewrite run_class: execute new hooks for setUpClass, run, tearDownClass; add exception handling
• add missing assertNotIn method to TestCase class
• provide more detail when exceptions trapped for hooks
• fix traceback reporting for TestCase hook exceptions
• report traceback on exceptions outside assertrasises when running test methods
• fix AssertRaisesContext
• handle assertion failure that does not have any message