Detect auto-correlations via np.allclose, rather than equality

[sjperkins]

Closes #308

• Tests added / passed

  $ py.test -v -s africanus

  If the pre-commit tests fail, install and
  run the pre-commit hooks in your development
  virtuale environment:

  $ pip install pre-commit
  $ pre-commit install
  $ pre-commit run -a

• Fully documented, including HISTORY.rst for all changes
  and one of the docs/*-api.rst files for new API

  To build the docs locally:

  pip install -r requirements.readthedocs.txt
  cd docs
  READTHEDOCS=True make html

[landmanbester]

Unfortunately this didn't solve the problem. Dropping flagged rows (the auto-corrs are flagged in this case) seems to get me around the error though

[sjperkins]

Unfortunately this didn't solve the problem. Dropping flagged rows (the auto-corrs are flagged in this case) seems to get me around the error though

Another way this bug could manifest is if max_fov=0.0, but by default this is set to max_fov=3.0.

[landmanbester]

I've left it to the default in this case. Let me try to create a reproducer then we take it from there