Release GIL during resampling

[richardsheridan]

CFFI implicitly released the GIL by default when calling into libsamplerate, whereas pybind11 keeps the GIL by default. This change in 0.2.0+ leads to major GIL contention in a application where I was successfully getting thread-based parallelism before.

I don't have much experience with pybind11 but it seems {py::gil_scoped_release release; ...} blocks will be needed around calls to src_simple and others.

[tuxu]

Very good point and definitely an oversight. Would you mind giving PR #14 a try?

[Bentroen]

Was looking exactly for this – I'll be giving it a shot and report back on the results :)