NFFT package

This is a package for calculating FFTs at nonequidistant nodes. This operation is also called Gridding and often used in medical image reconstruction (e.g. in MRI). This package is actually quite old and my first attempt to compare Julia with C. In the end the Julia version is in about a factor 1.5 of the nfft3 C library.
I made some cleanups and think that it now can be part of the package list.

Would be great if I also could have push access to METADATA.jl so that Pkg.publish() works. Thanks!