This add the notmuch version and absolute path of the binary used
in the pytest header. This is nice when running the tests
interactively as you get confirmation you're testing the version you
thought you were testing.
This introduces CFFI-based Python3-only bindings.
The bindings aim at:
- Better performance on pypy
- Easier to use Python-C interface
- More "pythonic"
- The API should not allow invalid operations
- Use native object protocol where possible
- Memory safety; whatever you do from python, it should not coredump.
