support pbr based setup

[mvk]

• dynamic versioning + semver
• use tox

Signed-off-by: Max Kovgan [email protected]

[mvk]

do not forget to export BASECRM_ACCESS_TOKEN env variable before running: tox or python setup.py test

[mvk]

summary

added pbr:

1. using setup.py forces you to manage version.py file, like in the 90s. and forces to bump versions manually.
2. using pbr allows to bump versions as easy as adding a tag. tag by default needs to be MAJOR.MINOR or MAJOR.MINOR.PATCH, added tox: easy virtualenv creation, tests running, etc. your CI now only needs to run 'tox' :-)