this is a interactive rebase of PR #1384
dropping unrelated commits and fix minor merge conflicts
more docstring improvements
Removed local path
Renamings and docstring fixed
Added comments to release notes
Style edits per Josef's comments; adde FactoredSPDMatrix class and de…
Added solve and logdet methods to FactoredPSDMatrix class
Minor docstring edits
should be ready for green button merge, when TravisCI reports back.
Coverage remained the same when pulling e891fe0 on josef-pkt:cor_nearest_1384_rebased into cd7f0d0 on statsmodels:master.