Compatibility fixes and code formatting

Compatibility fixes and LGPL license

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

Fixed
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-   psy-reg is now officially licensed under LGPL-3.0-only, see [#9](#9)

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

Changed
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-   Documentation is now hosted with Github Pages at <https://psyplot.github.io/psy-reg>. Redirects from the old documentation at [https://psy-reg.readthedocs.io]{.title-ref} have been configured.
-   Examples have been removed from the psy-reg repository as they now live in a central place at <https://github.com/psyplot/examples>
-   We use CicleCI now for a standardized CI/CD pipeline to build and test the code and docs all at one place, see [#8](#8)

Add the fitting of generic model classes

New release for python 3.7

New release inline with psyplot v1.1.0

First official and stable release