moved pesi exported fxns to sep files, pesi file now with global man file and helper fxns closes #324
fixed some pesi file names misspelled, #324
added more docs for worms fxns, closes #308
added more documentation for pesi_* fxns, including pesi_gen_iface fxn and pesi_iface data object
now exporting pesi_gen_iface inline with worms_gen_iface avail to user