Implement IResampler using Libzita-resampler

[gavv]

We have IResampler interface that abstracts sample rate conversion backend. There are two major implementations: hand-crafted BuiltinResampler, and SpeexResampler that uses SpeexDSP library.

Now we need to add another implementation, ZitaResampler, that will use Libzita-resampler library (home page, documentation). The implementation would be pretty similar to SpeexResampler.

New resampler should be added to ResamplerMap. Also it should be added to the list of tested backends in test_resampler.cpp.

Note that our resampler interface allows to change frequency ratio smoothly and dynamically via set_scaling() method. This is so because we use resampler for clock drift compensation. See this page for more details on how resampler is used. See also #235 for some background and rationale.

[novertia]

Hi @gavv can I pick up this issue

[gavv]

Sure, thank you!