master
fix: (1) Fix some buggy display result in tooltip, like 2 value axis scatter, add add test cases for them. (2) Buggy results in tooltip.renderModel: 'richText' for each cases. And add test cases for them. (3) Add styles to renderMode: 'richText', make them the same as renderMode: 'html'. (4) Make `tooltip.confine` default `true` if `tooltip.renderMode` is `richText`. And fix the positioning of it to avoid to overflow the container, which will be cut. (5) Fix the `tooltip.formatter` callback in `renderMode: 'richText'`, previously the concatenating rich text by `params.marker.content` does not work. (6) Refactor the implementation of `Series['formatTooltip']`: Add a abstract layer named `TooltipMarkup` to describe the tooltip layout requirement for each series, instead of lots of messy code to concatenate `html` and `richText` in each series. `TooltipMarkup` is responsible for generating `html` or `richText` finally. Add `TooltipMarkup` is also in charge of sort the tooltip by `valueAsc`, `valueDesc`, `seriesAsc`, `seriesDesc`.
test: fix UT.
tweak: Clarity the previous implements of axis statistics.