Document release procedure
Add changelog entry for v2.0.0

And add changelog entries, in general, to the long description
that will be uploaded to PyPI.
Ensure MANIFEST.in is up to date

Using the `check-manifest` script, which is now configured in
`setup.cfg`.
Remove examples/spa_sequence-Class.ipynb

This no longer reflects the way that we recommend that people
make SPA models. It also failed due to the ummagification of networks.

Accordingly, I renamed `examples/spa_sequence-Context.ipynb` to
`examples/spa_sequence.ipynb`.
Fix benchmark and optional tests.

- Added plotting to `test_thalamus`, and modified thresholds
- Pretty sure in `test_cache_performance` there's supposed to be a
  big relative timer difference using the cache...
- Pass args on in `test_decoder_solver_extra`
- Adjust tolerance in `test_compare_solvers`; some are not great
  when the signal is up near 1.
- Fix `utils.compat.is_number`; we changed `is_integer` to check for
  `np.integer`, but not `is_number`. This is required for
  `test_regularization`, which passes in a `np.int64` for `n_neurons`
Accommodate Numpy types in `is_number`

`is_number` can now detect all Numpy floats and complex.