#135 - HAL embedded resources are now rendered as collection by default.

To get consistent representations rendered for single-item collections and multi-item collections, we now use an enforceEmbeddedCollections flag in the Jackson 2 HAL module. Adapted HalEmbeddedBuilder to respect that setting and exposed it via the HandlerInstantiator for user level customization.

Changed RelProvider.getSingleResourceRel(…) to getItemResourceRel(…).