Wrong fraction of cluster area reported

[Gabriel-p]

See bh87coord with semi mode and:

bh87coord      1082.       1290.        750.        10      1   1   0   0

The reported fraction of cluster area is 1.01 where it can never be larger than 1.

See:

1. https://math.stackexchange.com/questions/2417849/portion-of-square-area-within-a-circle
2. https://stackoverflow.com/questions/622287/area-of-intersection-between-circle-and-rectangle
3. https://stackoverflow.com/questions/540014/compute-the-area-of-intersection-between-a-circle-and-a-triangle
4. https://math.stackexchange.com/questions/261336/intersection-between-a-rectangle-and-a-circle

[Gabriel-p]

This was fixed using a simple Monte Carlo algorithm here 7d2fda6