Removes relying on ActiveSupport::Inflector for case conversions. Since

Inflector is used within Rails
(https://github.com/rails/rails/blob/master/activesupport/lib/active_support/dependencies/autoload.rb#L38) autoload this can adversly effect that
feature. Instead, convert ACRONYMS to regex and apply directly to
::Hash.from_hash. Also, remove a backwards_compat spec and convert it
into a general purpose spec.