Corrected Wald test and correct results

The Wald test doesn't need the n (you were right), and we somehow got rid of the inverse at one point. Also, we can use ginv to calculate the generalized inverse of sigma and have no singularity issues. I think that the alternative U2 calculation looks good. I think we're done!
Merge pull request #7 from mattybeam/patch-7

Corrected Wald test and correct results