Release 2.2.0

• Add support for Ruby 2.4
• Change most remaining interfaces to use keyword options. (Change most of the remaining options = {} to **options.)
• Change implementation of #to_hash to #to_h and deprecate #to_hash. This is required because #to_hash is an implicit accessor, which causes problems for methods using keyword options.
• Deprecate Enumerator#to_ary and Statement#to_ary
• Add Literal#to_str for string-like datatypes

As methods taking keyword options implicitly try to turn the last argument into a hash (using #to_hash), this problem can be avoided by ensuring that the last argument is always a hash (empty if necessary). This mostly affects URI#initialize, and Query#initialize.

Array() uses implicit #to_ary. As this pattern is fairly pervasive, DEPRECATION warnings are not issued. In a future release both #to_ary and #to_hash will be removed entirely, which will make interfaces more consistent. The plan is for this to be done in a future 3.0 release.