Refactor the build system and package generator
    
    - Modernize the packaging by using PBR and setuptools;
    - Introducing metadata inside setup.cfg;
    - Using tox;
    - Unittest on python 3.5, 3.6, 3.7;
    - Remove module version;
    - Remove toml file (pyproject.toml);
    - Using PEP 516 (Build system abstraction for pip/conda etc) instead of PEP 518 (Specifying Minimum Build System Requirements for Python Projects);
    - Introducing requirements files
    
    Co-authored-by: Hobbestigrou <hobbestigrou@erakis.eu>