[plt-scheme] FrTime as a library

Hi Dave,

> I was wondering if there is an equivalent mode for FrTime? For
> example, I'd like to be able to do something like this:
>
> [...]
>
> I guess this might possible by requiring a few files like "frp-
> core.ss" from the FrTime collection. However, I'm not sure which ones
> I need and which I don't.
>

There is currently no such library, but most of the signal-processing
procedures are in lang-ext.ss.  frp-core.ss is mostly low-level stuff
that you shouldn't need (except super-lift, which is the basis for
most switching).

Greg