Poetry support (Python 3.10)

[hute37]

In order to include this package in pyenv/poetry (3.10) setup, I've made some changes in build environment

• cleanup dependencies: only six is required (for six.string_types)
• fixed setuptools problem in poetry install: Poetry install error #12
• moved dev dependencies to requirements-dev.txt (added requirements-ide.txt for emacs/lsp support)
• added pyproject.toml as alternative root detection pattern
• minor fixes (pytest, type checks)
• added GitHub actions for test, lint and package
• bumped version to 0.2.1

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test result are available here:

• https://github.com/hute37/python-rootpath/actions