Add separate ENABLE_PYTHON{2,3} cmake options
This MR closes #228 (closed) by adding ENABLE_PYTHON2 and ENABLE_PYTHON3 allowing people to opt in to the python modules (rather than opt out).
This MR closes #228 (closed) by adding ENABLE_PYTHON2 and ENABLE_PYTHON3 allowing people to opt in to the python modules (rather than opt out).