add_axis: Add an axis to a timeline plot
In timelyportfolio/timelineR: Interactive Timelines

Often, a timeline plot needs an x axis, so this little function supplies a very thin wrapper for d3.svg.axis, so that we can add it to our timeline htmlwidget.

add_axis(chart = NULL, scale = NULL, orient = NULL, ticks = NULL,
  tickValues = NULL, tickSize = NULL, innerTickSize = NULL,
  outerTickSize = NULL, tickPadding = NULL, tickFormat = NULL,
  styles = NULL)

`chart`	timeline plot htmlwidget to which you would like to add an axis
`scale`	scale
`orient`	orient
`ticks`	ticks
`tickValues`	tickValues
`tickSize`	tickSize
`innerTickSize`	innerTickSize
`outerTickSize`	outerTickSize
`tickPadding`	tickPadding
`styles`	styles