[Pas2js] Chart class added

[Michael Van Canneyt]

Hello,

Silvio Clecio contributed a ChartJS unit, which contains external class
definitions for the chartjs library:

https://www.chartjs.org

I added the unit and the demos (lots of them: 17 !) to SVN.

You can see the demos and code in action on:

https://www.freepascal.org/~michael/pas2js/chartjs/index.html

The sources are viewable for each demo.

A huge thanks to Silvio for this very useful contribution :)

Michael.