* move solveTriangular*() to TriangularView::solve*()
* move .llt() to SelfAdjointView
* add a high level wrapper to the efficient selfadjoint * vector product
* improve LLT so that we can specify which triangular part is meaningless
=> there are still many things to do (doc, cleaning, improve the matrix products, etc.)
* add an efficient selfadjoint * vector implementation (= blas symv)
perf are inbetween MKL and GOTO
=> the interface is still missing (have to be rethougth)