Vectorization (SIMD) of Vector

Use OpenMP to vectorize some operations in Vector. The class is a little bit messier now because I cannot use lambda function with OpenMP. 
A minor remark: Can we move the allocate() and deallocate() functions to the vectors.templates.h file (and move this include there as well)? We need these methods for compilation of vector.cc and we will not gain in speed (expensive calls to malloc/free), so no need to make them inline. If that is done, I will merge.