Minor release supporting Vega 5.7.

Additions

• Multi-line titles and spacing (tiLineHeight, axTitleLineHeight, leTitleLineHeight).
• Subtitles and associated customisation (tiSubtitle, tiSubtitleColor, tiSubtitleFont, tiSubtitleFontSize, tiSubtitleFontStyle, tiSubtitleFontWeight, tiSubtitleLineHeight and tiSubtitlePadding).
• tiEncodeElements and associated teTitle, teSubtitle and teGroup for dynamic customization of title elements.
• maLineBreak and maLineHeight for multi-line text marks.
• Legend symbol limit (leSymbolLimit).
• trDotBin transform and associated property functions (dbroupBy, dbStep, dbSmooth, dbSignal, dbAs) for dotplot binning.
• trQuantile transform and associated property functions (quGroupBy, quProbs, quStep, quAs) for quantile generation.

Deprecations

• tiEncode deprecated in favour of tiEncodeElements.

Other Changes

• Restructured API documentation to use better thematic grouping of functions with tables of contents.
• Documentation indicates titles can span multiple lines via a strs array.
• Some additions to the test gallery for new distribution transformations (dotplot, quantile plot).