Arbitrary Rank Update to Cholesky Factorization

Solves the Cholesky factored system with arbitrary update.

Solves Ax=b where A is given in terms of its Cholesky factors plus an arbitrary nonsymmetric, low rank update.

A=R'*R+U*V'

Where R is n by n and U and V are n by r.
Useful in solving finite and spectral element discretizations of boundary value problems.