Async support

[eyeseast]

Geopy has a set of tools to help with async here: https://geopy.readthedocs.io/en/latest/#async-mode

Should definitely use those, especially when thinking about Datasette integration.

[eyeseast]

What does this look like in code?

Geopy strongly recommends using a context manager for async calls. And geocode_row right now requires a geocoder function (because of rate limiting). There's a lot to manage here.

Rate limiting example here: https://geopy.readthedocs.io/en/latest/#geopy.extra.rate_limiter.AsyncRateLimiter

It's very possible I'll need to collect all the arguments for everything up front, and then sort everything out. That's messy.

[eyeseast]

Thinking about this more, especially after spending more time with faster services like OpenCage, Google and Mapbox, I should probably decide whether this is a sync or async library overall. Being in both places is probably too much to manage.