add polyphonic sampler

[DBraun]

This is a polyphonic sampler that works like the VST chugin (#47) I developed earlier. So you can do
sampler.setParameter(0, 60./127.); // set to center C because the 0th parameter happens to be the center frequency of the sampler.

Then if you do sampler.noteOn(60, 1.); then you'll get the original sound. If you did sampler.noteOn(67, 1.); it would be pitched up and sped up. The interpolation is good too.

Most importantly you can load samples!
sampler.read("C:/path/to/drum.wav"); // absolute path

You can enable/disable the amplitude envelope and filter envelope. You can also control the ADSR of both of these envelopes. The filter has a parameter for its base cutoff frequency and another parameter for how the filter envelope modulates it. All of these parameters are subject to change as Sampler grows, so chuck users should be careful about updates in which the parameter order might change...

There's also the issue of the vst_patch.patch that I put in the root directory (same as mentioned in the VST PR). I think chuck itself needs to change so that strings can be returned by chugins.

[DBraun]

Once the Faust chugin supports polyphony this chugin won’t be worth merging.

[DBraun]

Closing because I think the polyphonic Faust PR makes this unnecessary.