Support for FFTs

This wraps the FFTW library to do FFTs in libdynd.
Sometimes I need a fundamental function that libdynd is missing -- in this instance, concatenate. Usually I will try and implement it properly. Rarely, like in this case and for rand, I will put a quick stopgap in so I can move on with the bigger picture. Concatenate is an example of this. It needs to be done properly at some point.

This version works for a pair of 1D arrays.