get inspiration from js viz libraries

[maxheld83]

there's a lot of dev going on here with ever more r wrappers.

• Echarts
  • Upstream: https://echarts.apache.org/en/index.htm
  • R wrapper: https://github.com/JohnCoene/echarts
• Vega
  • Upstream: https://vega.github.io/vega/
  • R wrapper: https://github.com/vegawidget/vegawidget