add autocorrelated process error back in

[aappling-usgs]

removing autocorrelated process (pc) error stan models as of 10/14/16 == #264 == 1f2a4d9 to simplify and because we may not need pc for the first paper. someday i'd like to add it back in.

[aappling-usgs]

i think this is done/successful. won't be the fastest-running models, but they should work just as well as they did before. still not planning to use these models in the first few papers, though - too slow to converge.