vega.preview and vega.data.preview commands and iconography refinements

+ new panel icons for each preview type

added json language configuration for json vega files mapping

v6.2.0

added json lang. config

updated built-in vega and vega lite examples

see new/changed vega specs in #37 updates

vega libraries update and new 📈 commands and shortcuts iconography

see tickets #37 & #40 for more info

added data preview restore on vscode reload

see #31 for more info

data preview docs and screen pics patch release

Updated extension readme.md with new bits about alpha csv and json data preview panel and screen pics.

alpha data preview panel release

see #30 for more info

updated vega lib and examples to v5.4.0

• added new regression vg.json examples
• updated violin-plot.vg.json and probability-density.vg.json examples
• updated total built-in vega and vega lite examples count in readme.md

see vega v5.4 release notes for more info:

https://github.com/vega/vega/releases/tag/v5.4.0

updated embeded vega-lite lib and examples to v3.21

see vega-lite release notes for more info: https://github.com/vega/vega-lite/releases/tag/v3.2.1

preview panel toolbar UI refinements

see #29 for more info