`Neighbors` doesn’t seem to work properly across the antimeridian

[samritchie]

Calling Neighbors on a hash that abuts the 180th meridian returns incorrect values:

> GeoHash.Neighbors "rb";;
val it : string [] = [|"rc"; "rc"; "rb"; "pz"; "pz"; "px"; "r8"; "r9"|]

It appears to shift the NE, E & SE neighbours one hash west, presumably it’s somehow truncating the longitude to 180?

[jesseemerick]

Interesting. I'm not sure I'm going to have the time to look into this. I'm actually no longer actively using this library. I'd definitely take a PR with tests. Also there's a couple of forks that may or may not be more actively maintained. Thanks!