Create an example with streaming data

[ThomAub]

Vega-Lite allow a chart data to be updated. See this example Streaming Data or this other one with websocket

It would be nice to have a small example with a web server displaying a graph with streaming data.

Possible examples ideas:

• A visualisation of the different step of the K-means algorithms in Linfa
• A public API that post time series updates

After some experimentation I think that this could be the start to think of an higher level of abstraction as it requires some additional features in show_vega.rsto build other type of resulting html.