Document minimum and maximum

[Reconcyl]

Could the crate documentation be updated to specify what the exact bounds on noise output values are? Experimentally, two-dimensional OpenSimplex noise values appear to always lie in the range [-0.544, 0.544].

Related: #51

[nic-hartley]

This would be very helpful. Some quick experimentation suggests Perlin noise is nearly always between -0.5 and 0.5, but not quite actually always. If it was normalized to some standard range, like 0 to 1, this library would be much easier to use. If the limits were documented anywhere, even.

[bsurmanski]

From code comments, the range is supposed to be between -1 to 1 for most noises. I believe the current ranges are a bug. I fixed the perlin ranges here: #283

[AideTechBot]

I agree, the fact that all the noise functions seem to have random max/mins is kinda annoying.