update color op example
update mol docs

include docs for addResidue/addChain/addAtom and add some
introductory material on how to create views.
fix transparency after drawing a picking scene
add code to show bounding spheres

This code is meant for debugging of the auto-slabbing code.
pull auto-slabbing code out of viewer
fix auto-slabbing when molecules are off-center

Closes issue #45.
a little more reasonable defaults for fog
Merge branch 'master' of https://github.com/biasmv/pv