Add more examples

[wybert]

Add more examples for different types of plots listed in the document,

julia> plot.<TAB>
# bar                 barpolar            box                 candlestick
# carpet              choropleth          choroplethmapbox    cone
# contour             contourcarpet       densitymapbox       funnel
# funnelarea          heatmap             heatmapgl           histogram
# histogram2d         histogram2dcontour  icicle              image
# indicator           isosurface          mesh3d              ohlc
# parcats             parcoords           pie                 pointcloud
# sankey              scatter             scatter3d           scattercarpet
# scattergeo          scattergl           scattermapbox       scatterpolar
# scatterpolargl      scattersmith        scatterternary      splom
# streamtube          sunburst            surface             table
# treemap             violin              volume              waterfall