def get_field(name)
      @fields ||= {}
      field = fields[name]
      raise Tripod::Errors::FieldNotPresent.new unless field
      field
    end
def get_field(name)
      @fields ||= {}
      field = fields[name]
      raise Tripod::Errors::FieldNotPresent.new unless field
      field
    end
Return the field object on a +Resource+ associated with the given name.

 @example Get the field.
   Person.get_field(:name)

 @param [ Symbol ] name The name of the field.