This is all internal stuff for now.

* remove non-existant reference to CwiseAll
* define \householder_module (used in HouseholderSequence.h)
* update I01_TopicLazyEvaluation.dox - Product is now called GeneralProduct
* remove reference to list of examples which was deleted ages ago
* rename PartialLU_solve.cpp snippet to PartialPivLU_solve.cpp

* add a HouseholderSequence class (not good enough yet for Triadiagonalization and HessenbergDecomposition)
* rework a bit AnyMatrixBase, and mobe it to a separate file