Refactor to allow matrix structure in covariance matrices to be exploited
Improve handling of linear algebra issues; add options to fine tune iterations
Fixed typo NOne -> None
Minor renaming and docstring edits
Minor typographical changes
Minor docstring and naming changes, ready to merge
Merge pull request #1643 from kshedden/gee-linalg-refactor2

REF: Allow matrix structure in covariance matrices to be exploited