Create a Leslie matrix.
Given the length n array of fecundity coefficients f and the length n1 array of survival coefficents s, return the associated Leslie matrix.
Parameters :  f : array_like
s : array_like


Returns :  L : ndarray

Notes
New in version 0.8.0.
The Leslie matrix is used to model discretetime, agestructured population growth [R30] [R31]. In a population with n age classes, two sets of parameters define a Leslie matrix: the n “fecundity coefficients”, which give the number of offspring percapita produced by each age class, and the n  1 “survival coefficients”, which give the percapita survival rate of each age class.
References
[R30]  (1, 2) P. H. Leslie, On the use of matrices in certain population mathematics, Biometrika, Vol. 33, No. 3, 183–212 (Nov. 1945) 
[R31]  (1, 2) P. H. Leslie, Some further notes on the use of matrices in population mathematics, Biometrika, Vol. 35, No. 3/4, 213–245 (Dec. 1948) 
Examples
>>> leslie([0.1, 2.0, 1.0, 0.1], [0.2, 0.8, 0.7])
array([[ 0.1, 2. , 1. , 0.1],
[ 0.2, 0. , 0. , 0. ],
[ 0. , 0.8, 0. , 0. ],
[ 0. , 0. , 0.7, 0. ]])