new-ui todo

 - Widget show/hide
   - Continues to contribute to layout
   - Receives Update()
   - Does not recieve events or Draw()

     - Contributes layout == leaves gaps
     - Enable/Disable that doesn't contribute layout either?
     - "Slide" animation - gradually increasing layout?
     - So we end up have different overlaid regions for different phases.
     - Needs some brainstorming about regions.

 - Check header documentation against implementation.

 - TextureFont should only measure/render single line spans (remove
   newline/paragraph handling)

 - Review class structure and use of friend classes.
   - Combine Widget and Container?

 - Sliders should handle clicks either side of button.

 - Use unsigned ints where appropriate.

 - Grid rowspan/colspan. AttributedWidget.

 - Clean up inclusions. Should mostly only need to include Context.h.

 - Check that all container adds/removes issue RequestLayout().

 - Scroller needs to calculate travel from inner widget height.

 - Scroller should take mouse input from the entire inner area, not just that
   covered by the inner widget.

 - Should boxes preserve aspect?

 - Make console handle UI.Foo
   - Generalise LuaObject dispatcher and have it call in


ANSWERED:

 - Why does Scroller not inherit from Single?
   - Because its not a Single. It has two widgets inside.

 - Are mouseup/down and mouseactivate/deactivate fundamentally different?
   - Up/down has position.

 - Does Image need STRETCH_MAX scaling? Is there a time where scaling
   shouldn't be aspect-aware?
   - Yes, backgrounds.

 - Scissor should be queryable so that widgets can choose not to do expensive
   draw ops that will just be clipped (MultiLineText).
    - Except that its really fiddly. Premature optimisation?