Port the oids module to CFFI
Use gssapi.bindings package, not gssapi.headers

bindings contains code to detect GSSAPI features and initialise cffi.
Update .gitignore and requirements.txt
Port names and error modules to cffi.
Port creds module to cffi
Port ctx.py (context-related functions) to CFFI
Use cffi in setup.py, incl/exclude the right files
Remove unused line
verify() actually doesn't accept unicode arguments
We really don't need to be too clever guessing types

Every implementation I've seen uses pointer types for gss_name_t, etc.
GSS_S_BAD_MIC isn't defined in MIT Kerberos

It's deprecated and GSS_S_BAD_SIG should be used instead.
Erm, how did I miss this ...
None is not convertible to NULL anymore in cffi
Fix completely wrong usage of name_buffer
Because we're importing everything in setup.py, setup_requires everything
Make sure the MechName is valid-ish
Make the integration tests runnable
Change mentions of ctypes in doc to describe cffi
test for context lifetime
Python 3 fixes