Clarified the code structure for Rails.
Merge pull request #612 from edelgado/master

Clarified the code structure for Rails.
regex validator refuses params with nil value
Merge pull request #614 from dm1try/refuse_params_with_nil_by_regex_validator

regex validator refuses params with nil value
Update minimum version of Hashie::Mash, fixed performance issue with requests carrying a large payload, #494.
Expanded test matrix to more rubies.
Upgraded Rubocop to 0.20.1.