[X] Add AxisQuantitative/AxisTemporal to ConfigurationProperty: these were added in version 4.2.0 of Vega Lite.
[X] Add Header[Column|Facet|Row]Style to ConfigurationProperty
[X] Add ImageStyle to ConfigurationProperty (v4.0)
[X] Add BoxplotStyle, ErrorBandStyle, ErrorBarStyle to ConfigurationProperty
[X] Replace ConcatConfig and FacetConfig by CompositionConfig
[X] Add RepeatStyle, which uses the new CompositionConfig type
[X] Rename config properties for some degree of consistency
Autosize, Background, CountTitle, FieldTitle, Legend, NumberFormat, Padding, Projection, Range, Scale, TimeFormat, View now end in Style
note that I'm not plannig to do this to the Axis* constructors (at least not in this PR)
[X] split out Fill and Stroke options to replace 'Maybe Color' by '* Color'/'No*' versions.
[X] update HeaderProperties to add HLabel, HLabelExpr, HLabelFontStyle, HTitleFontStyle, and HTitleLineHeight [well, I've pushed the commit, but I don't see it below...]
HeaderPropertiesto add HLabel, HLabelExpr, HLabelFontStyle, HTitleFontStyle, and HTitleLineHeight [well, I've pushed the commit, but I don't see it below...]