binomial random draws
[rnd]=bino_rnd(N,p,r,c)
* N = the # of trials (scalar)
* p = the probability of success (scalar)
* n = number of trials (scalar)
* r,c = size of random sample from binominal(N,p) distribution (optional; default = 1,1)
* rnd = (rxc) matrix of random draws from the binomial (N,p) distribution, equal to the number of successes in n-trials
NOTE: mean = a/(a+b), variance = ab/((a+b)*(a+b)*(a+b+1))