Added QCQPSolver, no implementation yet
automatic documentation update
Added CSparseCholesky linear solver
Added vertcat/horzcat/blkdiag for CRSSparsity (crssparsity_tools)
Implemented a naive version of SOCPQCQPSolver

Uses cholesky and hence assumes positive-definiteness. Positive semi-
definiteness is not enough.
automatic documentation update
Merge branch 'develop' into issue_674b
Concerning #674: Updated CSparseCholesky to new syntax