Argparse-manpage

* We newly provide `build_manpages.build_py` and `build_manpages.install`
command classes that are re-usable from `pyproject.toml`. No need to
provide `setup.py` because of `argparse-manpage`. Solved issue85.

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* The `prog=` specifier (in setup.py/setup.cfg/pyproject.toml) is now
better handled so it doesn't conflict with ArgumentParser(prog=..).
Fixes https://github.com/praiskup/argparse-manpage/issues/79

* The pyproject.toml parsing feature now depends on the python3-tomli library
instead of python-toml for "python_environment >3, <=3.10".

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* Incorrect dict access for --include support fixed.

* Provide useful AUTHORS section with e-mail from
Distribution.get_author_email() even if Distribution.get_author() returns
None.

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* A new `--include` feature, inspired by `help2man --include`.

* Allow overriding build date with SOURCE_DATE_EPOCH environment variable
in order to make builds reproducible. See this link for more info:
https://reproducible-builds.org/specs/source-date-epoch/

* The AUTHORS section was changed to more standard AUTHOR.

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News in v4

* The manual page generator logic is now separated from the 'build_manpages'
module (which provides setup.py integration helpers). Therefore the
argparse-manpage doesn't necessarily have to depend on setuptools.
Projects that want to integrate using 'setup.py' should though place a new
"extra" named 'argparse-manpage[setuptools]' into their set of build
requirements in project.toml file.

* The old 'build_manpage' command (!= 'build_manpages') is now more
isolated from the rest of the code, likely never loaded.

* the Manpage class API was changed in v3 so it required an additional
constructor 'data' argument. This change was reverted, and the only
argument is again the ArgumentParser object.

* The 'version' and 'description' options were fixed.

* New options 'manual_section' and 'manual_title' were added.

* The manual page now automatically generates a current date in headers.

* Several groff escaping issues were fixed.

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New in version 3

* New man page format: single-commands-section
* Add CLI and conf options for setting the output format
* Add CLI and conf options to explicitly specify %prog value
* Skip showing commands with help == SUPPRESS
* Avoid rendering docs for command aliases
* Print program name in upper case in header and footer
* The --author CLI option has changed, and takes arbitrary string
(typically 'Author Name <theexample.com>'), and newly can be specified
multiple times. Therefore, it now replaces the '--author-email' option.
The --author-email option is kept, but is just an alias to the --author
option.
* All CLI options can be specified also in setup.cfg
* Don't render AUTHORS and DISTRIBUTION if they would contain undefined values
* Remove '... was written by' from AUTHORS

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* Fixed the testsuite against the setuptools v60+

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