Python-anvil

- Fixed issue with `requests_toolbelt` (`gql` dependency) using an incompatible version of `urllib3`.
This caused an error of `ImportError: cannot import name 'appengine'` to be thrown.

- **[BREAKING CHANGE]** [`graphql-python/gql`](https://github.com/graphql-python/gql) is now the main GraphQL client
implementation. All functions should still work the same as before. If there are any issues please let us know
in `python-anvil` GitHub issues.
- Updated examples to reflect new GraphQL implementation and added `examples/make_graphql_request.py` example.

- **[BREAKING CHANGE]** Minimum required Python version updated to `>=3.7.2`

- Clearer version number support
- Add additional variables for `CreateEtchPacket` mutation
- Add missing `webhookURL` variable in `ForgeSubmit` mutation
- Add `forgeSubmit` example

- Added support for multipart uploads on `CreateEtchPacket` requests.
- New example for multipart uploads in `examples/create_etch_upload_file_multipart.py`
- Added environment variable usage in all `examples/` files for easier usage.
- Updated a few minor development packages.

- Added support for `version_number` in PDF Fill requests.