doc: add noise documentation stubs

doc/noise.asc

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+== noise
+
+=== fractals
+
+fbm:: fractional brownian motion. simple summation of successive basis iterations with geometrically varying amplitude and frequency. results in homogenous and isotropic fields.
+hetero:: heterogenous fractal terrain. dampens high frequency contributions at local minima 
+rmf::
+hmf::
+
+runtime::
+
+==== fractional brownian motion (fbm)
+
+==== hetergenous fractal terrain
+
+==== ridged multi-fractal
+
+==== hybrid multi-fractal
+
+=== parameters
+
+octaves::
+
+H:: fractal hurst parameter.
+
+amplitude::
+gain::
+
+frequency::
+lacunarity::
+
+
+=== basis
+
+worley::
+perlin::
+value::
+patch::
+constant::
+
+=== lerp
+
+linear::
+cubic::
+quintic::
+cosine::
+
+=== turbulence