Allow use of `synth` inside synthdefs + JPverb

[defaultxr]

This PR includes the JPverb UGen, simplification of full-pathname, and the ability to use synth inside synthdefs.

Example:

(defsynth :mdapiano ((gate 1) (freq 440) (vel 100) (random 0.1) (rel 0.9) (stereo 0.3) (amp 0.5))
  (let* ((sig (/ (mda-piano.ar freq :gate gate :vel vel :release rel :stereo stereo :random random :sustain 0) 2))
         (ds (detect-silence.ar sig 1.0e-4 :act :free)))
    (declare (ignore ds))
    (out.ar 0 (* sig amp))))

(defsynth :tremolo-piano ((gate 1) (freq 440) (amp 0.5))
  (out.ar 0 (* (sin-osc.ar 8 0 0.5 0.5)
               (synth :mdapiano :gate gate :freq freq)
               amp)))

Caveats(?):

• The synth form will not automatically grab the values of its arguments from the synthdef; they have to be specified. This is similar to how regular function calls work though so it is probably more intuitive this way, albeit maybe less convenient in some cases.
• The embedded synth's unprovided arguments are not automatically promoted to arguments of the enclosing synthdef. This differs from SuperCollider's SynthDef.wrap functionality, but again, it is probably more intuitive this way since we are just calling synth and not a synthdef-wrap function or similar.

[byulparan]

wow....embeddable synth looks very useful!