Enrich2

Minor changes:

* Fix error when not specifying trim length https://github.com/FowlerLab/Enrich2/issues/73

Minor changes:

* Fix errors when adding SeqLibs https://github.com/FowlerLab/Enrich2/issues/70

* Fix an error when trying to create multiple orphan SeqLibs

Enrich2 now runs on Python 3 and is installable via [PyPI](https://pypi.org/project/Enrich2/).

Major changes:
* Updated to work on Python 3. The code has been most extensively tested on Python 3.12 but other versions should also work.

Minor changes:
* Fixes a long-standing [bug](https://github.com/FowlerLab/Enrich2/issues/44) with empty counts CSV files being generated for Experiment objects.
* Uses [fqfa](https://github.com/countess-project/fqfa} to handle FASTQ files instead of its own internal code.
* Many small changes due to the Python 2 to 3 conversion.

Minor changes:
* Fixed https://github.com/FowlerLab/Enrich2/issues/34
* `enrich_cmd --version` now outputs only the version number.

After careful consideration of community feedback, Enrich2 will now be distributed under the permissive BSD 3-clause license.

Major changes:

* Relicensed from GPLv3 to BSD 3-clause.
* Overhauled logging to ensure compatibility with messages generated by other modules.
* Updated installation requirements so a fresh install is possible with the current version of conda.

Minor changes:

* Made some minor code changes to keep pace with updates to pandas and matplotlib.
* Numerous changes to tidy up the code, such as fixing whitespace and removing unused imports.
* Small updates to installation documentation.

Minor changes:
* Fixed bugs that prevented the use of custom amino acid groupings.
* Set matplotlib backend to "Agg" when running inside a Docker container. Previously, generating plots from inside a Docker container would throw an error.
* Updated version requirements to ensure Python2 versions of dependencies are used.