Auto-generated cython_numpy wrapper

I added a new wrapping experiment 'cython_numpy_auto' that adds cython code auto-generation for the same approach as 'cython_numpy'.

To test drive:
* Auto-generate the cython code by running `python cython_generator.py` in directory `cython_numpy_auto`
* Install the wrapper with `python setup.py install --user` or similar command.
* Run the test with `python test_erfa.py` in directory `tests`.

Note:
You must have the `erfa` sources installed next to `erfa-wrapping-experiments` for the auto-generation to work.

To Do List:
- [ ] Automate structure generation/conversion from `erfam.h`
- [ ] Generate full API wrapper from `erfa.h`
- [ ] Integrated the templating engine `jinja2`
You already did! :)
https://github.com/liberfa/erfa/issues/24