Astroalign

In this release:

* Fix bug (65) that would cause register to fail when it's passed a Image object (from pillow)
* Migrated unit tests to Github Actions

In this release

* Added support to work with color images.

Check the details in the [documentation](https://astroalign.readthedocs.io/en/latest/tutorial.html#images-with-rgb-channels).

In this release:

* The functions `register` and `find_transform` now work with `CCDData` and `NDData` input.
* Docstrings and documentation changed to reflect the change.
* Added more exhaustive tests for new kind of input.

In this Release

* Keyword argument `detection_sigma` to control the std-dev above noise used in source detection. Default now is 5 instead of 3.
* Keyword argument `max_control_points` to control how many bright sources should be detected on an image.
* Keyword argument `min_area` to control minimum number of connected pixels of sources detected. Defaults to 5.
* Docs examples for few sources on the field.
* Docs examples for faint sources.
* Other code improvements.

Bug fix:

Very similar triangles made from very near stars may cause multiple correspondences between stars.

* Added a purge where only the best correspondence (min trasnsf error) is kept.
* Added test for this specific case.