Button to download an example

[aglitchman]

It would be great to example a direct link to download a specific example as it is, without downloading the whole examples project.

The download button can be placed under the "github" button:

Related issue - defold/examples#53

[aglitchman]

It turns out that GitHub doesn't provide an option to download individual folders as a zip.

To implement such a button, it seems to be easiest to zip all example folders in advance (automatically) and put them next to the example.

[aglitchman]

Also, we can zip all example folders and upload them to the Release page! I think it's the best option.
Then update the website and add links to the zip files.

[britzl]

Zipping the examples one by one is easy to do as a step in update.py when we process the examples. The zip archives can be put on the website.

The other solution would perhaps be to have a GitHub action in defold/examples which zips the examples, commits them to a release and then triggers a site rebuild.

[britzl]

Examples now have a download button.