Add `outLength` to full API, tells caller how many samples were written

[tortis]

Includes both number of frames and number of samples for convenience and to avoid confusion.

Real-world example usage:

const outLength = {frames: 0, samples: 0};
resampler.full(res.samples, sampleBuffer, outLength);
res.samples = sampleBuffer.slice(0, outLength.samples);

Ref #143

[aolsenjazz]

I'm glad that you brought up the idea of frames. It seems truer to implementation of SRC internally to use frames rather than samples. Would you revise to just use frames? Again, thanks for suggesting that.

Edit: Unless you think there's a compelling use case for including samples in the object. I just don't see it atm.

[tortis]

Sounds good, I amended the commit, so it just has frames now.

[aolsenjazz]

Thanks - 1 more step. I had to update node version in CI for tests to pass - would you merge with main and update to 2.1.2? I'll publish on NPM and worry about test coverage when I have some time.

Thanks for the extra time.

[tortis]

I rebased the upstream, and ran npm version 2.1.2. I can't push the tag to the upstream, if you wanna keep version tags, so I'll leave that to you.

Thanks for helping get this change out!