Start working on improving synths:

* Improve consistency of arguments - all trigger synths should have:
  - note
  - amp
  - pan
  - attack
  - release
  - [optional unique args]*
  - out-bus

* Add new modulated trigger synths:
  - mod_saw
  - mod_dsaw
  - mod_sine
  - mod_tri
  - mod_pulse

* Make all frequency arguments for synths MIDI notes:
  - notes
  - detune values
  - mod_range values
  - cutoff values
  
* Make all trigger synths stereo and accept a pan argument
* Make mono sample synths stereo (by adding pan argument)
* Modify mixer to assume stereo input
* Remove experimental synth designs