* add a LDL^T factorization with solver using code from T. Davis's LDL library (LPGL2.1+) * various bug fixes in trianfular solver, matrix product, etc. * improve cmake files for the supported libraries * split the sparse unit test * etc.
- remove some useless stuff => let's focus on a single sparse matrix format - finalize the new RandomSetter
* add unit tests for sparse cholesky