Add API endpoint GET /api/examples.json

[tbreuss]

Create API endpoint GET /api/examples.json adding a corresponding JSON file that includes certain front matter data from the files within the examples directory.

Instructions to do so can be found here: https://dev.to/mattwaler/creating-json-files-with-eleventy-13lk.

The API endpoint musst be:

• GET /api/examples.json

The data from front matter must include:

• title
• date
• tags
• level
• version
• authors
• credits
• links
• content without markup (if possible)

The goal is to have an API with several endpoints (in the end) starting with this one.

[tbreuss]

First version see #25