Restructure package to use the sunpy package template

[wtbarnes]

See https://github.com/sunpy/package-template. This provides helpers for generating docs and tests as well as helpers for setting up continuous integration.

The OpenAstronomy packaging guide is also a helpful resource: https://packaging-guide.openastronomy.org/en/latest/#

Additionally, this will make the installation process much smoother and will also make adding the package to PyPI/conda easier in the future.

[wtbarnes]

This looks like its mostly done. The last thing would be to switch to using tox for testing which would make the CI setup easier and make it easier to test multiple Python versions locally.