Automatically recurse into arrays

This teaches Fuse how to treat arrays, allowing for "to-many" relationships. The only way to do this currently (I think) is to use `getFn` to combine fields into a single string. That feels like a hack since it would return incorrect results based on how you combined the fields. (For example, if you did something like `fields.join('|')`, searching for `val1|val2` would yield a false positive.

All existing tests are passing and I added one for the new functionality.