Added MAD and biweight estimators to stats
Updated the names of the biweight estimators to biweight_midvariance
and biweight_location.   Fixed an error in MAD related to compare
a None to 0.
updating typo in funcs.py that was causing a crash
update of funcs to try to fix documentation issues
Updated funcs.py to fix doc issues
Merge pull request #621 from crawfordsm/master

Added robust statistics to stats