* Implement some missing `ui/` schemas
- Add `allow_debug_missing_texture`
- Add `propagate_alpha`
- Add `use_child_anchors`
* Tweak descriptions of `item_ref`
It should be noted that UI are referred to as "elements."
Moreover, the examples used colon (`:`) instead of dots (`.`) which contradicts the given description.
* Add more enum values to the `easing` property
These are all known values, aside from the five that was given.
