Include this Module for Value Object semantics

The idea is that instances should be immutable and compared based on state

  (rather than identity, as is typically the case)

@example

  class GeoLocation
    include Virtus::ValueObject
    attribute :latitude,  Float
    attribute :longitude, Float
  end

  location = GeoLocation.new(:latitude => 10, :longitude => 100)
  same_location = GeoLocation.new(:latitude => 10, :longitude => 100)
  location == same_location       #=> true
  hash = { location => :foo }
  hash[same_location]             #=> :foo