There two functionalities in this file
1/ Set the points of a polygon in the correct order so that no two lines intersect exept at the points
Creat a new class with eg. x = CoordinateSystemTools((x0,y0), (x1,y1), (x2,y2), (x3,y3))
The order is corrected automatically
2/ Find if a point is inside of polygon of n sides
x(x,y) returns a boolean