Added StrokeBuilder tool to support more complex brush shapes, plus:
- #18 Improved canvas rendering performance.
- #19 Modified uncommitted eraser stroke to render using panel background color, not white.
- #21 Promoted
RoundRectangleTool arc size configuration property to PaintTool.
- #22 Made anti aliasing mode configurable via
PaintToolBuilder#withAntiAliasing(...)
