Pypi release and better documentation

[gaelvila]

• edited pyproject.toml
• LICENSE file
• Repository structure have been modified for Pypi.
• Sources are in src/vip_client and distinguished between classes and utils
• Packages and namespace secured through __init__.py files.

  from vip_client import VipSession

• Documentation moved in doc/
• Examples reworked to import vip_client from Pypi and not src/
• Binder configuration files edited and moved in binder/

[gaelvila]

Binder instances to be put on test