Use data from URL for documentation

[roaldarbol]

Currently the package is being massively inflated by the data that lives in the package. The alternative is to host the data elsewhere (https://github.com/roaldarbol/movement-data). However, there's a few hurdles:

• Currently, it fails the reader validation checks
• Exceptions need to be written in those validators
• New validators need to be written for URLs

I have already substituted the data used in tests for minimal 20-line versions that live in tests/data.

[roaldarbol]

Actually just need to do this for documentation; for tests I use the header and like 10 lines of data.