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. 
I didn't know it was not portable, it's sad since OpenMP does not depend on the architecture :( In C++11, there is std::align but it's not implemented in gcc 4.9 and it just made to boost 1.56. I'm going to move allocate and deallocate and open a bug report to use std::align when it is a little more widespread.