Lookup up timezones for quadrangle areas

[ghost]

Right now, it's only possible to look up timezones for point locations.

It would be nice to be able to look up timezones for a rectangular area (e.g. a bounding box/quadrangle). I could see three possible interfaces for this:

1. If the area is completely contained within a single timezone, return that timezone; if not, return "Etc/UTC".
2. If the area is completely contained within a single timezone, return that timezone; if not, return whichever timezone has the most coverage within the area.
3. Always return an array of all timezones covered by the location. (In the case of a point, this will always be a list of length 1; in the case of an area, the array will be of length >= 1.) If we want to be really nice, this list could be sorted by amount of coverage within an area.