New nfft package

[Marco Caliari]

Dear maintainers,

NFFT (https://www-user.tu-chemnitz.de/~potts/nfft/) is a C library to 
perform the Nonequispaced FFT, released under GPL2. It has a Matlab 
interface (through mex). With a small patch to the configure script, I was 
able to install it in Octave. I also created a simple package. When you 
install it, the patch is applied and the library is compiled together with 
the Octave interface. You can test the correct installation by running one 
of the four test files (m-files) provided by the library.
At this point, if you know how to use the original C library or the 
original Matlab interface, with this package you can use it in Octave, 
too.

If you think it can be interesting for Octave, I would like to post the 
package on https://sourceforge.net/p/octave/package-releases/ (I think I 
need some authorization).

Best regards,

Marco