[semver:minor] Compatibility fixes and LGPL license

As with psyplot 1.4.0, psy-simple is now continuously tested and deployed with CircleCI.

Fixed
-----
-   Compatibility fixes for matplotlib\>=3.3

Added
-----
-   psyplot does now have a CITATION.cff file, see https://citation-file-format.github.io

Changed
-------
-   psy-simple is now officially licensed under LGPL-3.0-only, see [#28](#28)
-   We use CicleCI now for a standardized CI/CD pipeline to build and test the code and docs all at one place, see [#27](#27)

Author: Chilipp

.circleci/config.yml

@@ -1,7 +1,7 @@
 version: 2.1
 
 orbs:
-  psyplot: psyplot/[email protected].24
+  psyplot: psyplot/[email protected].25
   mattermost-plugin-notify: nathanaelhoun/[email protected]
 
 executors:

CHANGELOG.rst

@@ -9,6 +9,10 @@ Fixed
 -----
 - Compatibility fixes for matplotlib>=3.3
 
+Added
+-----
+- psyplot does now have a CITATION.cff file, see https://citation-file-format.github.io
+
 Changed
 -------
 - psy-simple is now officially licensed under LGPL-3.0-only,