Now defaults to Cholesky decomp for inversion, adds config parameter for using SVD which can invert singular matrices.

Adds checks in chi2fromcov for negative on diagonal elements, currently
ignores if using SVD.

Adds shapecovardecomp option following: https://arxiv.org/pdf/2003.00088.pdf
Use SHAPE/NORM in type option.

Adds shapecovars to T2K 0Pi AnaI and II

Adds manual remasking for AnaII that skips 0 bins. Matrix is still
sadly singular.