2D Radial Distribution Function

Calcs RDF with boundary conditions.

Inputs:

dr = width of shell within which it is searched for particles

maxRadius = maximum radius until whihc to calc RDF

coordinates = [X, Y] of size N*2, w´here N is the number of particles

ROIMask = Mask that indicates where exactly the RDF should be calculated. Only coordinates that have the minimum distance 'maxRadius' to the boundary of 'ROIMask' are considered for calculating the RDF in order to account for boundary problems