pfft 0.1

[jerro]

> I think that poor precision is a problem. I have checked now and
> std.numeric.Fft does indeed use floats for the lookup table.
> The precision problem could be solved by either changing that to
> real or by changing Fft to a template and using whatever the 
> type
> parameter is. Just changing float to real doesn't require 
> changing
> the API, but would probably result in worse performance.

I forgot to mention one more solution (the one that pfft.stdapi 
currently uses). The class could also use lazy initialization. 
When the fft is called, check if the lookup table for that type 
is already created, create it if it isn't, store it for later and 
then compute the fft. This would  require casting away const in 
the fft() method, though.