Changed
- [**breaking change**] In functions `format(field, format)` and `line(template)` in
tooltip builder, the '$' symbol is no longer used in aesthetic reference. It was replaced by the '^' (hat) symbol
(see the udated doc: [Tooltip Customization](https://lets-plot.org/pages/tooltips.html)).
- The project upgraded to Kotlin v1.4.10 (was v1.3.72).
Fixed
- No tooltip on v-line [[229](https://github.com/JetBrains/lets-plot/issues/229)]