Fix crash in help page display when command name is too long
Image::Filter::Smooth: allow use of types other than float

This is useful to allow operation on e.g. complex types
Image::threaded_copy: allow copying onto different types

This works as long as compiler can perform implicit type conversion
between the input and output image types
Math::Vector: fix use of legacy Math::ceil()
New Image::Filter::fft() function for in-place FFT