Value noise updates

[readmodifywrite]

API updates:

3 options for signature in noise() function:

noise(offset)
noise(offset, scale)
noise(offset, scale, start, end)

Internally:
offset is just index into noise array.
scale is a fractional multiplier times the offset.
so, n = noise(offset * scale)
then we map n onto the range of start -> end.

This moves common operations into C.