Large improvements to the DrawableSet structure
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-Addition of GameDrawableInstance to allow per Entity draw options on
drawbles
-Added informative docstring to DrawableSet
-Other Improvements
Moved Shapes and FRectangle to new Geometry namespace
Added GetBoundingBox method to Entity
Removed Proxy LoadAnimationXML method from Entity
Added OnScreen property to Entity
Refactored all code to explicitly state its Units
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-Properties and functions now state if the result will be in
-Pixels (px)   graphics coords
-Tixels (tx)   tile coords
-Rexels (rx)   relative coords