added specn.gradient variable to be read in from Master Simulation matrix which specifies whether speciation rate varies across the gradient ('on') or not ('off'); if it does, it varies linearly with the temperate-most bin having 1/10th the default (tropical) speciation rate
added two fields to the Master Simulation Matrix: specn.gradient and specn.factor which specify whether there is a gradient in speciation rates and by what factor rates at the tropical end are greater than rates at the temperate end; also made sure speciation is dictated by regional rates rather than a blanket rate as done originally.