Added `compile_downloads` to the package to provide methods to convert a list of downloaded sites to a single large `data.frame`.  Renamed `compile_list`, changing it to `compile_taxa` so it is clearer.  Fixed a small problem in `get_download` so that it doesn't balk at empty datasets.

TODO:  Develop an internal function in `get_download` so that it can download from a list of datasets.
Formatting changes to meet Google R style guide.

Merge branch 'master' of https://github.com/SimonGoring/neotoma

Conflicts:
	R/compile_list.R