sunpy 4.0 release candidate

[David Stansby]

Dear all,

The SunPy developers are pleased to announce the first release candidate for version 4.0 of the sunpy core package, sunpy 4.0.0rc1. We upload release candidates before a major release to allow users and developers of downstream packages to test their code and report any issues before the final release.

To install using pip run:

> pip install sunpy --pre

We would be greatful if you could report any issues you find at https://github.com/sunpy/sunpy/issues. Assuming there are no major issues found, we expect to do a full release of 4.0 on Fri 13th May.

Enjoy!

David Stansby

(on behalf of everyone who has contriubted to sunpy 4.0)