NEWS.md
You can interpolate objects from your R environment into vegajson and vegayaml code chunks using ${} as delimeters.
Added functions vegadown() and vegadown_labels() to access vegaspecs created using vegajson or vegayaml.
Added knitr engines for vegajson and vegayaml (vegayml); these are activated when the package namespace is attached. These become languages you can specify in RMarkdown code-chunks; they render the code as vegawidgets.