Improved Approximation

Issue 0001275 brought up the drag on a sphere.  This turned out to be a non-issue, however; the approximation could be improved (See source).  Also I am submitting the pull request here despite how the guide says to contribute code since the Unsupported Contributions Repository contains no source code, and has not been touched in months.  Let me know if it should go somewhere else.

http://web2.clarkson.edu/projects/subramanian/ch301/notes/dragsphere.pdf