change return types of decomposition methods for Cholesky decomposition to ICholesky and ICholeskyLDU
fix tests for -- change return types of decomposition methods for Cholesky decomposition to ICholesky and ICholeskyLDU
removed _getVV method from cholesky classes
immutable CholeskyLDU - change decompose method to static, add private constructor, use private instance of CholeskyLDU
immutable CholeskyLDU - fix CholeskyLDUSolver
immutable Cholesky - change decompose method to static, add private constructor, use private instance of CholeskyLDU, fix tests
remove public solveL_special and symmRankTranA_sub methods from Cholesky, fix doc