added FIS, MAR layers for Global2012.www2013 (#33), and deleting extraneous files in layers* folders within data_create.R script
fixed MAR functions, added dplyr dependency
resolved #52 by updating trend lm() calculation to use ddply with custom function vs summarize() argument. not sure why or at which versions stats::lm() or plyr::ddply() changed to dissallow the old method.