Pypuppetdb

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This is a maintenance release.

The major version is bumped because of:
- dropped support for PuppetDBs < 5.2.0 (Puppet 4 has reached its end-of-life in October 2018),
- dropped support for Python 3.6 (end-of-life in December 2021),
- the required [Requests](https://requests.readthedocs.io/en/latest/) version bumped to the current latest.

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- Remove harmful terminology, following [the Puppetlabs components name changes](https://puppet.com/blog/removing-harmful-terminology-from-our-products/) ([#216](https://github.com/voxpupuli/pypuppetdb/pull/216))
- Use built-in unittest.mock instead of mock ([228](https://github.com/voxpupuli/pypuppetdb/pull/228))
- Build and test dependencies updates.

Thanks to the following contributors of this release: [pgajdos](https://github.com/pgajdos).

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- Fix TypeError exception thrown by `BaseAPI._query()` when using debug logging.

Thanks to Ben Roberts for his contribution!

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- Python 3.10 added as a supported version
([213](https://github.com/voxpupuli/pypuppetdb/pull/213))

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- Added PQL support with `pql()` method
(PR [201](https://github.com/voxpupuli/pypuppetdb/pull/201),
fixes [167](https://github.com/voxpupuli/pypuppetdb/issues/167))
- Added ability to specify additional queries when using `Node.facts()`
([127](https://github.com/voxpupuli/pypuppetdb/pull/127))
- Improve the documentation (even more ;))
(PR [206](https://github.com/voxpupuli/pypuppetdb/issues/206),
fixes [143](https://github.com/voxpupuli/pypuppetdb/issues/143)
and [129](https://github.com/voxpupuli/pypuppetdb/issues/129))
- Fixed creating `Edge` objects
([202](https://github.com/voxpupuli/pypuppetdb/issues/202))
- Python 3.9 added as a supported version
([203](https://github.com/voxpupuli/pypuppetdb/pull/203))

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- Added support for `with` statement
([185](https://github.com/voxpupuli/pypuppetdb/pull/185))
- Added explicit `disconnect()` method
([185](https://github.com/voxpupuli/pypuppetdb/pull/185))
- Improved the documentation on [Read the Docs](https://pypuppetdb.readthedocs.io/en/latest/)
and in the project's README
([190](https://github.com/voxpupuli/pypuppetdb/pull/190))