feat(tooltip): click to show line tooltip

[pearmini]

支持可以通过点击展示 tooltip，主要的使用方式如下：

chart.on('plot:click', ({ offsetX, offsetY, target }) => {
  chart.emit('tooltip:show', { offsetX, offsetY: 20, target });
});

• code
• tests
• docs
• example

[coveralls]

Pull Request Test Coverage Report for Build 9709369272

Details

• 9 of 9 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.008%) to 86.388%

---

Totals
Change from base Build 9708207158:	-0.008%
Covered Lines:	10414
Relevant Lines:	11674

---

💛 - Coveralls