LEC: Largest Empty Circle between Points in a flat plane
also know as Pole of Inaccessibility problem.


see: https://en.wikipedia.org/wiki/Largest_empty_sphere
The largest empty circle problem is the problem of finding
a circle of largest radius in the plane whose interior
does not overlap with any given point and whose center
is lying in the convex hull of the points.

Hint: The LEC is centered at the Voronoi vertice of
the polygon which
(1) is located within the polygon and
(2) has the largest shortest distance of
    all internal Voronoi vertices to the polygon 

Parameters
----------
points : 2d numpy array with x, y coordinate of the points
         on the Concave Hull

Returns
-------
LEC_Radius: scalar
LEC_Centroid: (x, y)