add example playground

[thierryH91200]

In addition to #2335 with markup

It's very good as tutorial

[liuxuan30]

wow, thanks so much for your various help and contribution

[codecov-io]

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[pmairoldi]

This looks very cool! This should remove people asking why isn't there a swift demo.

[liuxuan30]

@petester42 swift demo support involves several PRs, do you think we could manage to merge them to reduce @danielgindi overhead?

[thierryH91200]

@petester42
II think this is not a good idea
this is swift 3
see pieChart
it is better to remove it
and I return a PR in swift 4

[thierryH91200]

and other problem

Playgrounds

Known Issues
macOS playground execution may hang in the Running state with no results produced. This is more prevalent when changing pages. (32429211)
Workaround: Stop playground execution and rerun. If issue persists, close and reopen Xcode.

The liveTouchBar property of PlaygroundSupport is not supported. (31073754)

[pmairoldi]

Works for me. Swift 3 or 4 doesn't matter the interface of library is the same.

[pmairoldi]

If you want to make improvements then go ahead but it works with current master.

[thierryH91200]

ok thanks