Hubmap-api-py-client

- Adding support for cell type queries

- Adding new functionality for getting max value of data type (and optionally gene/protein)
- Updating documentation and tests to include queries by modality
- Updating doc tests for greater independence from index version

- Updating doc tests, adding new query type
- Add new parameter to enable gene->dataset and protein->dataset queries
- Running tests on client test server

- Version 8 was skipped

- Support iteration over result sets.
- Add python environments to gitignore.

- Parameterize api endpoint doctests.
- Only use POST, for simplicity.
- Use values_included appropriately.
- Values in error are sorted.
- Run tests in parallel.
- Remove `get_list` from external interface.
- Distinguish `ResultsSet` from `ResultsList`.
- Remove `values_type` parameter
- `ResultsList` supports `[]`
- Generate pydocs, with accurate kwarg lists..