Default Tooltip position should be relative to mouse cursor, not to mouse position

[creage]

Description

Widget part tooltips are hovered by mouse cursors, making tooltips not readable enough

Steps to check or reproduce

• Go to examples page https://naver.github.io/billboard.js/demo/#Chart.DonutChart
• Hover over chart part Expected: tooltip is fully visible Actual: mouse cursor hovers some part of tooltip, hiding tooltip content

[netil]

@creage, it mean tooltip not be hidden from cursor like Gauge type, right?

[creage]

@netil maybe. But better these tooltips behave like standard HTML title.