v2.0.0 — `{version_tuple}` write + onbuild placeholder, et alii

• The {version} placeholder in the "basic" format step has been renamed to {base_version}. The old name remains usable, but is deprecated.
  • Breaking: The version argument passed to Versioningit.do_format() and format method callables has been renamed to base_version.
• A {version_tuple} field, along with the fields available in the format step, is now available for use in templates in the write and onbuild steps.
  • New step and subtable: "template-fields"
  • Breaking: The version arguments passed to Versioningit.do_write(), Versioningit.do_onbuild(), run_onbuild(), and write & onbuild method callables have been replaced with template_fields arguments
  • Added a get_template_fields_from_distribution() function for use by callers of run_onbuild()
• Versioningit.get_version() now takes optional write and fallback arguments
• The onbuild step is no longer run when building from an sdist; the configuration therefore no longer needs to be idempotent
• Drop setuptools runtime dependency
  • setuptools is only needed for get_cmdclasses(), which should only be called in an environment where setuptools is already installed.
• Prevent log messages from being printed twice under recent versions of setuptools
• Values supplied for the require-match parameters of the tag2version and onbuild steps must now actually be booleans; previously, values of any type were accepted and were converted to booleans.
• Added a Versioningit.run() method that returns a structure containing all intermediate & final values
• "git" method: {author_date} and {committer_date} are no longer "clamped" to less than or equal to {build_date}. This undocumented behavior was based on a misinterpretation of the SOURCE_DATE_EPOCH spec, and was even applied when SOURCE_DATE_EPOCH was not set.
• When resolving entry points, if multiple entry points with the given group & name are found, error instead of using the first one returned