Add an example using the Python Prompt Toolkit

[deeplook]

The example should display a sparkline in a shell status bar using the excellent Python Prompt Toolkit. For thrills this should be a dynamically updated sparkline showing something like the CPU load value over time, updated once per second. I have to dig out some older attempt at this with code which was about 70% done...

Since I can't attach Python files here I've added some prototypical code as a gist. This dates back to May 2016, so it might need less prompt_toolkit imports today to achieve the same thing... But in principle it should be more of a real status bar that displays modestly on the lower window edge while one still can use the terminal as usual.