Typo fixes, whitespace removal, proofreading improvements, and more!

The important bits are probably:

- proofreading script can now take multiple files as input
- added DRC data to the canonical variables and columns
- added `--autocorrect-whitespace` to proofreading script, automatically fixes whitespace problems (as one might expect!)
- fixed whitespace/line ending issues across most data CSV files
- normalized a few names - `River Cess` became `RiverCess`, `Monteserrado` became `Montserrado`
- removed a bushel of `.DS_Store` and `Icon` files