Gammapy v0.13 release

[Axel Donath]

Dear all,

shortly before the summer break, we are happy to announce the release of Gammapy v0.13.

A big thanks to all contributors!

Gammapy v0.13 includes many bug-fixes a lot of clean-up work and some new features, e.g.

new models, more uniform handling of sky regions and support of binned simulations for 3d

as well as 1d datasets. A more detailed list of changes and new features can be found here:

https://docs.gammapy.org/0.13/changelog.html#july-26-2019

Instructions how to install / update Gammapy using `conda` and `pip` can be found here:

https://docs.gammapy.org/0.13/getting-started.html#install

https://docs.gammapy.org/0.13/install/pip.html

Please get in contact if you have issues with the installation or questions of any kind:

https://gammapy.org/contact.html

Have a nice summer, 

The Gammapy developer team