Better document plotlyjs.jl

[jdamiba]

In order to further adoption of the Dash For Julia project, it would be a good idea to document the functionality of the plotlyjs.jl package which users can interact with to create figures.

Work plan:

• port current examples to plotlyjs.ls from plotly.jl
  • rather than creating figures using the chart studio cloud API, figures should be rendered in place with plotlyjs
• figure out how to convert markdown documents which contain julia code to self-contained html
  • see plotlyjs.jl figures not rendering when exported as html JuliaPlots/PlotlyJS.jl#322 or https://github.com/sglyon/PlotlyJS.jl/blob/master/docs/build_example_docs.jl
• set up a plotlyjs.jl-docs github repository
• set up a CI pipeline to build the julia docs
• update this repo to pull in julia examples from the new repo.

[jdamiba]

cc @nicolaskruchten