Notable changes:

1. Dropping support for Python versions older than 3.7
2. Vendoring pip to get better reusable utilities since pip._internal doesn't look friendly
3. Fix dirty patches such as:

   pigar/pigar/core.py

   Line 31 in a608132

   _special_packages = {

4. MAYBE custom configuration file to work around #32
5. MAYBE rework the command line interface