ofNoise and ofSignedNoise with 2nd order control for rate.

[ofTheo]

ie: the equivalent of doing

float rate = 0.02 + ofNoise(ofGetElapsedTimeF() * 0.02, 100.0) * 0.015;
float value = ofSignedNoise( rate, x, y );

as one function.

also see kyle's #1134 for other noise utils.

I find myself needing this quite often for more natural random motion where the rate of change is variable.