Scale free network using B-A algorithm

Generates a scale free directed adjacency matrix using the BA algorithm

Use as:
A = BAgraph_dir(N,m0,m);
Where, N = number of nodes in the network, m0 is the size of seed network and m is the average degree of seed network; use mo=m or m<m0. For example,
A = BAgraph_dir(300,10,10);
The resulting adjacency matrix contains a 1 in row i, column j if i connects to j. A has a power-law in-degree distribution. Please be patient as the algorithm may take ~2-3 minutes to generate an adjacency matrix for N=300.