Live profile display

[mpickering]

It would be nice to be able to display a profile as it was being created.

1. Pipe the eventlog into a socket using - https://github.com/bgamari/ghc-eventlog-socket
2. Add a webserver to eventlog2html which can parse the eventlog data and convert it into a suitable JSON format.
3. The display page includes a button "start" which starts the process and connects to the local server via a websocket or whatever is used these days.
4. Modify the chart logic to accept the data for the chart incrementally - https://vega.github.io/vega-lite/tutorials/streaming.html