Improvements of example

[AGulev]

Would be great to improve example by adding one more layer for interactive elements like line and bezier.
When user move cursor we redraw this interactive elements on this extra layer, and put them to the main layer when user release cursor.
Of course we can use fill() for clearning "extra texture", but would be greate to save previous drawing (coordinates) every frame and before drawing new line, redraw old one with alpha (smaller fillrate and better performans than using fill() method)