First attempt at creating a more GeneralNames based  X509SubjectAltnativeName class

The tests will fail untill the X509_NAME_free and X509V3_EXT_d2i are exposed from the cryptography project.  This new get_subject_alt_name method will split up the alt Names into seperate components.


You can leave off "Test that ..." in test method docstrings - it's implied. :smile: 

What does it split up the general names from?  Into?  Lots of detail in test method docstrings is great because this is basically the specification.