Yarn-api-client

* Add support for Python 3.8.x.
* Fix HTTPS url parsing.
* Fix JSON body request APIs.
* Handle YARN response with empty contents.
* Better logging support.

This is a quick follow-on fixup release to 1.0. It includes the following:

1. Passes the authorization instance to the Active RM check (58)
2. Establishes a new (working) documentation site in readthedocs.io: yarn-api-client-python.readthedocs.io
3. Adds more python version (3.7 and 3.8) to test matrix and removes 2.6.

- Major cleanup of API.
- Address/port parameters have been replaced with complete endpoints (includes scheme [e.g., http or https]).
- ResourceManager has been updated to take a list of endpoints for improved HA support.
- ResourceManager, ApplicationMaster, HistoryServer and NodeManager have been updated with methods corresponding to the latest REST API.
- pytest support on Windows has been provided.
- Documentation has been updated.

**NOTE:** Applications using APIs relative to releases prior to 1.0 should pin their dependency on yarn-api-client to _less than_ 1.0 and are encouraged to update to 1.0 as soon as possible.

- Honor configured HTTP Policy when no address is provided - enabling using of HTTPS in these cases.

- Extend ResourceManager to allow applications to better determine resource availability prior to submission.

- Hotfix release to fix an internal signature mismatch