Size-transition dimensions and time variability

[jimianelli]

In Andre's version, GMACS now allows for different numbers of size-classes for males and females when computing the growth matrices (which automatically guarantees that the size-classes with non-zero abundance will differ between males and females). In addition, to mimic BBRKC model, GMACS now allows the size-transition matrix to change over time (with the possibility of different numbers of size-transition matrices by sex). Finally, to ease parameterization, the parameter that determines the variance of the growth increment can be parameterized as an offset (0 implying that the variance in growth increment is the same for more than one size-transition matrix).