Reorganize namespaces

For better organization in the YARD doc sidebar, element classes were
moved into the Iora::Elements namespace.

Previously, this was avoided because it required more typing. Now,
however, inspired by Fullscreen/yt, the Iora::Elements module is
included in the main Iora module, meaning that all element classes can
be referenced with either notation (Iora::Elements::Result and
Iora::Result refer to the same class).

I also moved Iora::Element to Iora::Elements::Element. Even though the
full module path is a mouthful, it will result in a cleaner top level
namespace, especially when associations are refactored into
Iora::Associations.
Refactor duplicate code in tests