+ Add cursor
The cursor location follows the mouse pointer movements when it hovers over the graph
and updates the coordinates of the cursor's cross-points in the graph legend.
- Update to moisseev/D3Evolution@c73017a039bfb1377627f7d116f7aa0df92ad219 :
- Fix X-axis scale
- [Fix] Do not draw paths through undefined regions
- [Feature] Display `null` values as colored areas
- Add `step` interpolation