[feature] adding multiple option support to String#to_region

@jgv thanks for providing this great gem!

I had a need to pull city and state separately from a zip code and I didn't want to do any string splitting or multiple searches. So, I added support for handling multiple options when calling `String#to_region` and I thought it might be useful to everyone. 

This change keeps the existing API intact with no changes, but now will return an array of results if you pass multiple options.

```ruby
"11211".to_region #=> "Brooklyn, NY"
"11211".to_region(:city => true) #=> "Brooklyn"
"11211".to_region(:city => true, :state => true) #=> ["Brooklyn", "NY"]
```