Add CSV support

[silasary]

This is terrifying, and not the greatest. However, it is very good for simple things, and I think a lot of people would get value out of it, especially when entering repetitive data.

This PR adds:

• Support for items.csv and locations.csv (The former is much more useful, but I'm not gonna stop people from using the latter)
• load_data_csv helper function. Hooks users will probably find this useful
• Finally adds a bugfix for when your category is a string rather than a list (Because CSV items will always be a single string)
• Option to use "classification": "progression" in your items. This lets you have a single column, rather than five.

This could definitely be improved. Off the top of my head:

• Special logic to lowercase headings/values that should be lowercase.
• Support for multiple categories
• Data Validation?

I wrote this on the train ride home from PAX, and was very sleep deprived at the time. Do we even want it?

[FuzzyGamesOn]

At some point, yeah, we want support for alternate formats. Our documentation needs to catch up before we do that, though, so people have a point of reference for the options regardless of format.

The classification option does seem useful on its own, though. Might be worth adding that in a separate PR in the meantime.

Also, once we get to adding alternate formats, Builder would need to be updated to support them.

[silasary]

Closing in favor of #96 #97 #98