updated vega-lite library and examples to v3.2 for previews

see #28 for more info

added local data support for concatenating views

see #26 for more info

also, updated vega libs, examples, schema and data to vega v5.3.5 and vega-lite v3.10.

retain theme selection on preview refresh patch

see #24 for more info

added vega-themes toggle to Preview

see #24 for more info

added/updated latest vega v5 & vega-lite v3 built-in examples

see #25 for more info

updated vega.js to v5.3.4 for the latest v5 bug fixes

see #19 for more info

updated vscode, ts & vega libs to latest

see package.json changes & #19 for more info

v3.2.1

#20 data transforms scans base case patch

added local data support for transforms and view spec compositions

see #20 for more info

added layered data local files loading support

see #15 fore more info