Fix get_index, add delay rate limiting, format with Black

[auralewd]

This uses a different and cleaner strategy for getting the volumes. should be nicer than #23

Also adds delay, to avoid being IP banned.

also formats the code with Black formatter.

[Patrick-Hogan]

I cherry picked some of the changes from this PR in alongside a different rate limiter implementation (same cli arg, though, so completely API compatible w/ what you wrote--but doesn't block the first call, and blocks based on time from start of call). Other than the separate ratelimiter implementation, I included basically everything that's still relevant after the many changes to the wanderinginn table of contents page, except for the black formatting (would have included it, but there were enough other changes it caused some minor headaches and I haven't gotten around to setting up black to run locally and/or in a pipeline to enforce formatting yet).