Fixed bug in chirp stimulus that led to amplitude being square of desired amplitude.
Got rid of all the "FillFromParams" methods, and all use of them.
Fixed inf's in PSC stimulus for time points well before onset.
Added the RNG seed as an explicit argument to the "white" noise stimulus.  This makes it so that all stimuli are deterministic and reproducible from their parameters.
Renamed "White Noise" to "Frozen Noise", b/c it's not necessarily white, and that makes clear that it's a deterministic function of the parameters.
Got rid of vestigial code that specified default stim params as floating-point instead of strings.
Added a stimulus type that uses interpolates from a wave in the root folder.
Added "Intended Workflow" and "Multiple Versions" sections to README.txt.
Updated README.txt is preparation for the 8.21 release.