Upgrade to easyfft v0.3

[WalterSmuts]

Unfortunately this requires an extra Default trait bound which results in requiring a major version change for fftconvolve.

Practically it's not an issue since all elements that you'd want to convolve would implement Default, but it's a bit annoying.

Default is required for initializing the scratch-buffer, which is strictly not necessary but requires changes to rustfft. It's currently pending this issue in rustfft: https://github.com/ejmahler/RustFFT/issues/105

[rhysnewell]

Easy as, but should this wait until that RustFFT issue is resolved or do you reckon it is good to go now?

[WalterSmuts]

I don't think the issue will be resolved anytime soon so I would recommend to merge for now. Unfortunately it means a major version change for fftconvolve so consumers would have to manually update to the newer version and resolve any conflicts. Since fftconvolve is still relatively young I don't think it's much of a concern. The chances for running into upgrade conflicts is also super slim since the only change is an added Default trait bound, which all applications would likely already conform to.

If the issue get's resolved, it would mean easyfft and fftconvolve could drop the Default requirement without a major version change.