closes#83, closes#84
- Issue #83: Add position tuple support to constructors
- Frame and Sprite now accept both (x, y) and ((x, y)) forms
- Also accept Vector objects as position arguments
- Caption and Entity already supported tuple/Vector forms
- Uses PyVector::from_arg for flexible position parsing
- Issue #84: Add pos property to Frame and Sprite
- Added pos getter that returns a Vector
- Added pos setter that accepts Vector or tuple
- Provides consistency with Caption and Entity which already had pos properties
- All UI elements now have a uniform way to get/set positions as Vectors
Both features improve API consistency and make it easier to work with positions.
