Make meanEdgeLength public in PoissonDiskSampler

[dyollb]

The parameter rCoeff in PoissonDiskSampler is used to compute the minimum distance between points

minDist = rCoeff * meanEdgeLength;

The value meanEdgeLength is computed by PoissonDiskSampler and stored as member. If I want to sample a surface with a known minDist I need to compute the meanEdgeLength myself in order to specify rCoeff as minDist / meanEdgeLength.
I would propose to add a getter to get the mean edge length, e.g.

class PoissonDiskSampler {
...
double getMeanEdgeLength() const { return meanEdgeLength; }
...
};

[dyollb]

fixed by #186 - meanEdgeLength is no longer needed to compute relative sample distance.