Bpc-poseur

* several bugfix in convertion
* implemented unittests
* updated Pipenv deps

* bugfix in convertion implementation
* implementing unittests

* implemented unittests
* added test samples
* revised `poseur.decorator`
* revised docstrings
* other minor updates

* revised setup.py
* fixed Homebrew formula

* implemented poseur (full functional)
* revised Makefile for distribution automation
* drafted README & manual
* reviewed PyPI setup scripts
* other minor misc stuff