| Module | CouchRest::Validation::ValidatesWithMethod | 
| In: | lib/couchrest/validation/validators/method_validator.rb | 
Validate using the given method. The method given needs to return: [result::<Boolean>, Error Message::<String>]
@example [Usage]
  class Page
    property :zip_code, String
    validates_with_method :in_the_right_location?
    def in_the_right_location?
      if @zip_code == "94301"
        return true
      else
        return [false, "You're in the wrong zip code"]
      end
    end
    # A call to valid? will return false and
    # populate the object's errors with "You're in the
    # wrong zip code" unless zip_code == "94301"
    # You can also specify field:
    validates_with_method :zip_code, :in_the_right_location?
    # it will add returned error message to :zip_code field