Initial work on covariancematrix
run go fmt

oops
add benchmarks
improve performance and decrease memory use
improve comments
only perform shorter benchmarks
use var in place of new
example implementation of pure go covariancematrix
simplify example implementation
implement tests for when there is no BLAS
improve godoc for CovarianceMatrix
add help for non-exported variance and covariance
split out non-blas impl into new function

Splitting out the non blas path makes the code flow easier to read.
go fmt
remove tests for non-blas code path
remove non-blas codepath

Also put ones directly into CovarianceMatrix function
implement tests for in place and weighted covariance
impl weighted cov matrix and in place assignment
expand on help text
add tests for covariancematrix panic