add cython extension to setup.py
add cython extension to setup.py

BruceSherwood/vpython-jupyter,sspickle/vpython-jupyter,mwcraig/vpython-jupyter,BruceSherwood/vpython-jupyter,sspickle/vpython-jupyter,mwcraig/vpython-jupyter,BruceSherwood/vpython-jupyter,BruceSherwood/vpython-jupyter,mwcraig/vpython-jupyter,mwcraig/vpython-jupyter