Vocoder 2.0

The main innovations are twofold: decoupling the vocoder code into several steps (calcuate freq bands, bandpass the signal, generate envelopes, generate carriers, reconstruct), and adding a poisson click train as a built-in option for the carrier.  Have a look, @rkmaddox, and see if (1) it works as expected, and (2) it is organized in a sensible way.  I'm happy to do some refactoring to make this optimally useable.  @Eric89GXL feel free to chime in too.  

No new tests as yet, and since I changed the name from vocode_ci to just vocode, the old tests will fail at the moment.
Yeah, we made that failure intentional as a (somewhat obscure) way to tell people to update their version of Pyglet. See:

https://github.com/LABSN/expyfun/commit/dd9c0e2fc46a82b5b8326d3278a50652dabea14f

Sorry for the confusion. Probably should mail this out to expyfun-users. And make that mailing list, actually...