MRIaggr-calcBlockW_cpp: Find disjoint spatial blocks of sites
In bozenne/MRIaggr: Management, Display, and Processing of Medical Imaging Data

C++ function called by calcBlockW to identify independant spatial blocks of sites according to a neighbourhood matrix.

1	calcBlockW_cpp(W_i, W_p, site_order, dist_center, dist_max, verbose)

`W_i`	the 0-based row numbers for each non-zero element in the sparse neighbourhood matrix. integer vector.
`W_p`	the pointers to the initial (zero-based) index of elements in the colum of the sparse neighbourhood matrix. integer vector.
`site_order`	a specific order to go all over the sites. integer vector.
`dist_center`	the distance between each point and a reference point. numeric vector.
`dist_max`	the neighbourhood range. numeric vector.
`verbose`	Should the process be verbose over iterations ? logical.