Add module with aggregated functions for this project (unfinished).

This module is created so that we may eventually clean up the current code a bit more and divide them into functions. Currently there are only functions to create pred-obs files for dataset/distribution combos. I've tested the function ```get_obs_pred_multi_dists()``` with Gentry data. It ran with no problem for logseries, geometric and Zipf. It choked half way through for negative binomial, but I probably won't have the time to track down the error before leaving town. Poisson lognormal is significantly slower than the others; it has thrown all sorts of warnings but has been running without choking so far.

Elita and Ethan, you are more than welcome to keep building/modifying/testing this module if you have the time/energy. I probably won't be able to resume the work until mid January. 

PS. I think the current _obs_pred.csv (for logseries) files are created with the parameter estimated from the untruncated logseries, but the predicted values obtained from the upper-truncated logseries, so we probably want to redo the analysis with the new code.