Add unit test of aperture mass calculation
Add unit test of Schneider ap mass
Only warn about OpenMP being unavailable if user specifically requests multiple threads
Move more tests to the if name==main slot to help reduce the running time of nosetests
Explain the derivation of the Schneider aperture mass calculation
Mention the unit tests in the README file
Add more about the new features in the CHANGELOG
Forgot to commit k2.params