Updated installation and documentation

Simplifies the installation process for nustar_pysolar and removes some some deprecated dependencies.

Updated the README files and added documentation via readthedocs (link on the README page). Note that lots of docstrings need to get fixed still, but it's at least usable.

Major thing is that this version contains an update HTML location to download the occultation files.

For now, I recommend starting in a completely fresh conda installation and download location for this repo to avoid any clashes with earlier versions.

Updated FITS file handling and master-->main

This release updates the handling of the FITS keywords to play nicely with updates to astropy so that sunpy maps are now properly generated.

As of this tag, the default branch has also been changed from master --> main.

To update your local branch from master-->main do the following:

git branch -m master main
git fetch origin
git branch -u origin/main main
git remote set-head origin -a

Now with more mosaics

Because we needed more mosaics.

v0.1: Merge pull request #45 from bwgref/master

Stable version for use with sunpy v0.8 and astropy v2.0