Added some new functions, changed the names of functions and fixed some bugs.

Lots of changes I guess.  Largely bringing the code up to a common style standard (borrowed from the Google R Style Guide).  Added a new `compile_downloads` function and changed `compile_list` to `compile_taxa`.

Fixed a small bug in `get_download` that caused an error if there was no count data.

New sites are rolling into Neotoma so we'll probably find more bugs along the way.