Add demo code.
Fix a name of function from renderer.span.destroy to renderer.span.remove.
Arrange positions of all grid after a span was rendered instead of after all spans were rendered.
Debounce calling the function for tuning.
Refactor a main logic of the view.renderer.
Merge pull request #62 from pubannotation/bugfix_over_span

Bugfix create a span over a existing span