Refactoring:
  - Port to CLIPS 6.40

Backwards incompatible changes:
  - Dropped support for Python 2
  - APIs reworked to better reflect CLIPS 6.40 changes

Issues:
  - issue #14: support PEP484
  - issue #38: fix constructs representation logic
  - issue #42: refactor constructs binary loading logic
  - issue #43: remove non ASCII characters from README
  - issue #44: fix Makefile

Build:
  - Support manylinux 2014 (PEP599)