Release notes for cobrapy x.y.z

New features

View number of genes in model notebook representation.
Add EMBL GEMs (https://github.com/cdanielmachado/embl_gems) to the list of repositories.

serializes GPRs to strings to avoid massive storage usage
Reformatted example files (e_coli_core.xml, mini_cobra.xml, mini.json, mini.yml, textbook.xml.gz) to be more compliant with identifiers.org.
ncbigi is not a valid identifiers.org, so it was replaced with ncbiprotein.
make sbml.py subsystem reading add partonomy, which matches the definition of SBO:0000633 (see https://sourceforge.net/p/sbo/term-request/113/)
Correct reading and writing of subsystem in mat.
General cleanup of code in mat.py
fix the pandas deprecation warning in find_external_compartment

Resolve flake8 issues and add missing type annotations and docstrings in src/cobra/io and tests/test_io (#1212).
Updated model.py and test_model.py to Python 3.6+, including type annotations and docstrings.
Resolve remaining flake8 issues and enable the check in GitHub Actions Lint workflow (#1272).

Removed model.add_reaction() and replaced remaining usages of it with model.add_reactions()
Removed the following tests: test_add_remove_reaction_benchmark, test_add_reaction, test_add_reaction_context, test_add_reaction_from_other_model, test_add_cobra_reaction
Removed model.__add__ and model.__iadd__ - use model.merge to replace them.
Remove Model().description().
Remove Model().get_metabolite_compartments().