Centroid

Notes:

Calculate the centroid and slopes for all apertures:
The structure of the return on the function is a row vector of slopes:
[s_x(0,0),.,s_x(0,N),.,s_x(M,0),.,s_x(M,N),s_y(0,0),.,s_y(0,N),.,s_y(M,0),.,s_y(M,N)]

Centroid calculation using thresholding method.

Interesting look construction. Do you need the i and j loops? And could you put this part inside a function (lets call it a `_create_mask()` function for instance?)