Add new FX: wobble:

* multiple control rate forms
* rhpf over an exponential range
* wave inversion
* phase offset

Awesome dubstep fun to be had! Also good with the amen break too:

use_synth :dsaw
sd = sample_duration :loop_amen

with_fx :wobble, mix: 0.5, phase: sd, wave: 0, invert_wave: 1, cutoff_min: 5, cutoff_max: 129 do
  loop do
    sample :loop_amen
    sleep sd
  end
end