Synonyms for grey vs gray

[orangejulius]

We should handle difference is spelling of grey vs gray with a synoynm.

We probably cannot rely on users to type the one that matches in a streetname, venue name, etc. In fact, over in pelias/api#1432 (comment) I found a case where OSM data uses one spelling for a street, and data from OA uses the other.

What are other English language words that have common spelling variants like this? We might want to handle them all.