Process all examples as integration tests

[katauber]

All examples are processed. If there is any exception, the tests will fail.
Closes #121

[katauber]

lein test is executed in the Github Actions, so on every push all examples will be processed

[fsteeg]

Here's what I noticed:

• It seems only the top-level examples are tested, not those in the experimental and workshop folders
• It would be nice to print the filenames of the examples to understand what's actually tested
• What's tested is just that they can be processed without throwing exceptions, right? Perhaps we could test a bit more, e.g. that the result is non-empty?

I gave it a go in 6b96c01, hope it's idiomatic.

We might even want to add the expected result as a second line to the examples, so we can compare the results?

[katauber]

I gave it a go in 6b96c01, hope it's idiomatic.

I moved the log message to when the example is really executed

We might even want to add the expected result as a second line to the examples, so we can compare the results?

I would like to see this in another issue, so we can merge this pull request :)