Added the possibility to use scopes with arguments, by passing a array or a lambda via the scopes option.
Added an option to use a specific action name.
Improved the extra_data option to handle hashes where the keys are the columns passed to select and the values are the names of the methods to be called or lambdas.
Made the arguments sent to extra_data lambdas the same as those sent to scopes lambdas.
Fixed tests arguments expectations for json_for_autocomplete and get_autocomplete_items methods.
Refactored parts of the json_for_autocomplete unit tests and made the 'with extra data' test check that the extra data attribute is actually returned.
Added tests for json_for_autocomplete with extra data as a Hash.
merged multi-field changes from slash4 pull request