Lona: Function Plotter Demo

Markus Gritsch created an amazing Lona demo, implementing a function plotter, using lona-chartjs.

It is an exciting day: This is the first community-contributed demo for the documentation ever!

Markus is a great guy, and we mailed a back-and-forth frequently, leading up to this. He helped a lot, debugging crashes on an iPhone 6, fixed many typos and issues in the documentation, did much proof-reading for the tutorial, and contributed many ideas for upcoming SVG-support in Lona.