Move datasets to generation/download/optional

[tms-bananaquit]

• datasets includes a couple of csv files that have to be included with the library to work properly right now, rather than being downloading as needed/being generated via script.
• The datasets are always included right now, since they're in a child of the src directory. The rainfall data is ~ 3 MB. If we aren't going to do one of the above, there's probably a clean way to fiddle with the setup.py s.t. that download is optional.