logisticGrowth function

This function is simply an implementation of the logistic growth equation where: f(x) = K / (1 + ((K - N_0)/N_0) *exp-k(x-x_0)) ; Where x_0 is an adjustment to the position of the midpoint of the curve's maximum value K = the curves maximum value, k = the steepness of the curve (growth rate), and N_0 is the starting population it includes parameters to change the midpoint as well as change the natural exponent (ie: exp) to some other value. NOTE: This is for continuous growth, and since SHAPE is discrete at present this is an unused function.