Move all calls to Pm_Write and Pm_WriteShort to one thread.
Move all calls to Pm_Write and Pm_WriteShort to one thread.

Instead of relying on users to use our library bindings thread safe, we instead
make the bindings themselves thread safe.  Since libportmidi itself isn't
thread safe, we now have only exactly one thread that calls native subs.

Perl6-Noise-Gang/Audio-PortMIDI