Add plot legends for 3D mode

[axkr]

Please add legends for complex parametric plots with colours and their corresponding values.

Example:

function z1(z) { try { return  inverseHaversine(z);}catch(e){return complex(Number.NaN);} }

var p1 = parametric( (re,im) => [ re, im, z1(complex(re,im)) ], [-0.3, 0.3], [-1.0, 1.0], { complexFunction: 'abs', colormap: 'complexArgument' } );