Support multi-type arrays containing Booleans in Coercer

[dennispatterson]

A multi-type array with a Boolean allowed type (e.g. 'attribute :multiple_birth, *Fhir::Type[Boolean, Integer]' in Patient) is really supporting instances of Virtus::Attribute::Boolean. The existing coercer allows an attribute to be of this type, but doesn't accept a value of true or false since those are instances of TrueClass and FalseClass, respectively.

Proposed updates:

• coerce_according_to_types / check_type! - when the allowed type is Virtus::Attribute::Boolean, allow for TrueClass and FalseClass.
• call - check the type of the coerced value so that a string like "true" can still be coerced into a boolean.
• virtus_coerce
  • Demodulize the type's name so that it looks for a "to_boolean" method on the coercer.
  • Rescue from an UnsupportedCoercion because coercers can't always coerce to a type just because they have a method to do so. Example: An integer coercer has a to_boolean method but can't coerce an integer such as 2.
  • True and false don't need to be coerced into booleans, so just return those values.