removed some cruft from Superpose3D()

It turns out that dividing the coordinates by the size of each point cloud (Rgf and Rgm) before superposition does not make the algorithm more numerically stable after all. So I removed the unnecessary and confusing code related to this bad idea.

BUGFIX: RMSD now calculated correctly when c≠1

RMSD is now calculated correctly when allow_rescale==True. (Equivalently, when c≠1. Note: The optimal rotation and translation are not effected. They continue to be calculated correctly. However the estimate of the RMSD was incorrect. Now RMSD is reported correctly.)

equations in setup.py corrected

I made some minor changes to the "long_description" argument in setup.py in order to make the equations for RMSD more clear. (I've been experimenting with how to convey these equations. These changes do not effect the behavior of the "Superpose3D()" function. They just change the way the equations appear at pypi.org. Each time I change something, I have to upload the changes to github and pypi to see how they appear online. That's why the last few releases have been so trivial.)

equations in documentation corrected

Some embarrassing mistakes in the equations from README.md and setup.py were corrected.
These changes should not effect behavior of Superpose3d().

features working

This is the first version of the software where I remembered to click on the "Draft a Release" button.