Invoke-release

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- [PATCH] Add configure_release_parameters to __all__

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- [PATCH] Fix classifiers

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- [MAJOR] Invoke Release now runs only on Python 3.7+. It can still release projects that use Python 2, but the ``invoke release`` commands must run on Python 3.7+.
- [MAJOR] Removed ``invoke wheel`` command.
- [MAJOR] Renamed plugin method ``version_error_check`` to ``error_check`` because it had nothing to do with versions.
- [MINOR] ``configure_release_parameters`` is deprecated. Please use ``invoke_release.config.config.configure``, instead.
- [MINOR] Performed a major refactor and re-organization of all internal code.
- [MINOR] Added Python type annotations.
- [MINOR] Added the option of supporting other source control providers in the future.
- [MINOR] Converted to a proper configuration system instead of saving config variables to individual global variables.
- [PATCH] Added considerable test coverage (>96% lines covered now)
- [PATCH] ReadTheDocs documentation.
- [MINOR] Fix 37

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- [PATCH] Properly handle + separator added in previous commit

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- [PATCH] Permit a + in the release version specifier

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- [PATCH] Fix GitHub PRs workflow when not pushing branch (33)
- [MINOR] Use parse_version instead of LooseVersion to properly compare versions