add keyword arguments to var and std
Merge branch 'master' into dh/cov2
new covm and cov implementations
cov tested
use unscaled_cov as core function
simplify the interface of covm and cov
add new corm and cor methods
cor & corm tested
export covm and corm
optimized implementation of unscaled_covzm
Merge branch 'master' into dh/cov2
new API for function cov
new API for cor
mean keyword argument for var and std
minor adjustment of API for cov and cor
minor adjustment of API for cov
Merge pull request #6273 from lindahua/dh/cov2

New implementation of cov/cor with extended API