Add wildcard as a supported token

## Feature Request
While doing some data wrangling, I have to parse a column of dates with a lot of date formats mixed in and extract the year part of those dates (Arrow has been of immense help!). However, there is a format that's quite peculiar: almost all instances of them conforms to MM-YYYY, but one instance has MM as 14 (which must have been a data entry error). The application I'm building is expected to be able to handle these kinds of data entry errors. I know I could fix it simply by switching to DD-YYYY or just use regex, but I believe that `arrow.get("14-2010", [..., "**-YYYY", ...]).year` would 1) best convey that I don't care about anything in the date except for year and 2) be more succinct than a bunch of if-else statements (which, I think, is the point of having arrow.get() accept a list of possible formats). I would work on this if you guys think this is a feature worth implementing rather than feature bloat. Thanks!