Further polishing:

* Removed MSVC-switch in tutorials and benchmarks for reading files (require users to run from build/ accross different OS)
* Updated old Eigen-code to version 3.x
* Fixed a few more warnings in Visual Studio, added /wd4996 flag to get rid of VC iterator advertisements
* Fixed an overly strict assert() on vector-reductions with OpenCL, including a clean initialization of reduction vector
* Changed STL overload of norm_X from enable-if to plain overloading, otherwise MSVC has problems.