Clawpack v5.7.0rc

[Randall J LeVeque]

I'm planning to officially release v5.7.0 (based on the current master branch, which is also tagged as v5.7.0) unless there are any last-minute changes.

There's a tar file at 

  https://github.com/clawpack/clawpack/releases

if anyone wants to try that out.

The new version of the docs are temporarily at

http://depts.washington.edu/clawpack/sampledocs/v570_docs/

See in particular

http://depts.washington.edu/clawpack/sampledocs/v570_docs/release_5_7_0.html

and please let me know if there's anything to add to these release notes.

The latest version of the gallery is temporarily at

http://depts.washington.edu/clawpack/sampledocs/v570_gallery/

Note some changes in how we build the docs,

I still need to fix up the Jupyter notebooks and most of those links are broken now, but otherwise all the gallery examples should be there with the exception of one pyclaw example.

Thanks to everyone who has contributed!

 - Randy