doc(site): add png export to on line playground

[sverweij]

Description

• Adds a quick and simple export to png & svg to the online interpreter.

Motivation and Context

• Easier than making screenshots

How Has This Been Tested?

• with eyeballs

(the online interpreter should b.t.w. graduated to use a normal framework like react/ vue/ svelte some day, to make it easier to test & maintain)

Screenshot

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• The code I add will be subject to The MIT license, and I'm OK with that.
• The code I've added is my own original work.
• My code follows the code style of this project.
• I have read the CONTRIBUTING document.
• [/] I have added tests to cover my changes.
• All new and existing tests passed.

[codeclimate]

Code Climate has analyzed commit 199ada1 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (100% is the threshold).

This pull request will bring the total coverage in the repository to 100.0% (0.0% change).

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