It is used in project documentation

Add a new entrypoint to simplify shell scripts

- handle git and mercurial as source or target
- add argument to indicate target branch
- add argument to specify target version system
- when pushing a new branch, also try the ancestor branches too rather than update on tip (was done when pushing to mercurial)
- add argument to set commit message on duplicated repository

 fix running python3.6 unittests

Document tox compatibility with 3.7

This makes the version used clearer.

[skip ci]

mercurial is already needed, but as an application, and used throught python-hglib

 update package classifiers

odoorpc has been released so no need to install from master in tests, and need to clearly indicate version in pyproject.

Extract version with setuptools-scm