Improve comment on what algorithm is used
Improve comment on normalization factor.
remove unused benchmark functions
change panic to use mat64.ErrShape
change benchmark constant names to lowercase

Changed SMALL, MEDIUM, LARGE, and HUGE to small, medum, large, and
huge, respectively.
correct weighted test, and make fixture clearer

Changed the names of the test table to be clearer.  Also made the
answer a matrix and used Dense.Equals instead of performing the
comparison on r, c, and the raw data.

Also, the old results for the weighted case were wrong.  I’ve added the
same items into the stat_test.go file.
Change to simpler impl

By taking advantage of some gonum functions, it is possible to remove
much of the code related to centering the columns.    Also tidied up
many of the comments.
go fmt