pull _slide* args out of doc arg table

Rather than crowding the arg table at the top of each synth/FX with the _slide, _slide_curve, and _slide_shape args, each "slidable" argument now has a note at the bottom with a clickable link to the generic slide documentation.

I would like to add pictures of each of the curves, but I don't think I understand them.  For instance, how many steps does the step curve have?  From my own testing, it seems to just jump to the target value instantly.