Fixes commitizen-tools#607

BREAKING CHANGE: Python 3.6 is not officially supported anymore. Please migrate from 3.6 to 3.7 or greater.

…one`

…with the tests

…ytest-freezer` removing warnings

…n loading

Plugins are now loaded using the `commitizen.plugin` entrypoint
while legacy plugin are not loaded anymore but a warning is raised when one is seen.

Fixes commitizen-tools#495

BREAKING CHANGE: Plugins are now exposed as `commitizen.plugin` entrypoints

… versions providers

…etry, Cargo)

…PM, Composer)

Reads version from the repository last tag matching `tag_format`

Fixes commitizen-tools#641

Topological ordering should be used when ordering commits in changelog history.
This allows commits to be shown properly in the order they were added to the codebase,
even if non-linear merges were used

…mmit-order

fix(commands/changelog): use topological order for commit ordering

Running tests concurrently can cause temporary files, such as the file
used to backup the commit message, to be deleted by one test but
accessed by another test later on.

…lease

feat(changelog): add merge-prerelease flag

…-tools#686)

* feat(bump): version_provider=semver optional option to make version compatible with semver

Signed-off-by: apkawa <apkawa@gmail.com>

* refactor(bump): version_provider rename to version_type; `pep` option rename to `pep440`

Signed-off-by: apkawa <apkawa@gmail.com>

* docs(bump): add `version_type` info to config.md

Signed-off-by: apkawa <apkawa@gmail.com>

* refactor(bump): to use VersionProtocol interface instead packaging.Version subclass

Signed-off-by: apkawa <apkawa@gmail.com>

* test(bump): `VersionProtocol` workaround mypy for py==3.7

Signed-off-by: apkawa <apkawa@gmail.com>

* fix(changelog): `changelog` command does not find version tag with `version_type=semver` option

Signed-off-by: apkawa <apkawa@gmail.com>

* refactor: minor review fixes

* test(changelog): fix test_changelog_incremental_with_merge_prerelease issue with freeze_time

Signed-off-by: apkawa <apkawa@gmail.com>

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Signed-off-by: apkawa <apkawa@gmail.com>