Python 3 support and better AstroPy integration

This release updates the deproject module so that it works with Python 3 - which is used by CIAO 4.11 - and the AstroPy ecosystem, as tabular data takes advantage of AstroPy's table support and the angular-diameter distance to a source now uses the AstroPy cosmology routines rather than calculating it directly. A number of enhancements and bug fixes have been made, including adding support for error calculation, plots, and tie-ing shells together (to reduce the effect of "ringing").

Documentation has been moved to the deproject read-the-docs page, and the GitHub page has moved to https://github.com/sherpa-deproject/deproject/.

A full list of changes is available at https://deproject.readthedocs.io/en/latest/changes.html#version-0-2-0

It should be installable into CIAO 4.11 with the following command:

pip3 install deproject

Registration on Zenodo is planned, but "technical complications" means that I am releasing the software first.

Version 1.0

Add README.rst