[semver:minor] Compatibility fixes and LGPL license

Fixed
-----
-   psy-view is now compatible with psyplot 1.4.0

Added
-----
-   psy-maps does now have a CITATION.cff file, see <https://citation-file-format.github.io>

Changed
-------
-   psy-view is now officially licensed under LGPL-3.0-only, see [#58](#58)
-   Documentation is now hosted with Github Pages at <https://psyplot.github.io/psy-view>. Redirects from the old documentation at [https://psy-view.readthedocs.io]{.title-ref} have been configured.
-   We use CicleCI now for a standardized CI/CD pipeline to build and test the code and docs all at one place, see [#57](#57)

.circleci/config.yml

@@ -1,7 +1,7 @@
 version: 2.1
 
 orbs:
-  psyplot: psyplot/psyplot-ci-orb@1.5.24
+  psyplot: psyplot/psyplot-ci-orb@1.5.25
   mattermost-plugin-notify: nathanaelhoun/mattermost-plugin-notify@1.2.0
 
 executors:

CHANGELOG.rst

@@ -6,6 +6,12 @@ Fixed
 -----
 - psy-view is now compatible with psyplot 1.4.0
 
+
+Added
+-----
+- psy-view does now have a CITATION.cff file, see https://citation-file-format.github.io
+
+
 Changed
 -------
 - psy-view is now officially licensed under LGPL-3.0-only,
@@ -28,6 +34,7 @@ Changed
   also the open figures, see
   `#47 <https://github.com/psyplot/psy-view/pull/47>`__)
 
+
 Added
 -----
 - A widget to control the plot type for mapplot and plot2d (see