Tests!

[fhammerschmidt]

Add a basic test runner, primarily to test all the file conversions end-to-end:

e.g. Input.json --> to DataSheet --> to Output.json --> check if Input & Output are equal
or Input.json --> to DataSheet --> mutate some text --> to Output.json --> check if equal besides the changed strings

[fhammerschmidt]

As a first step, we could add some example JSON files (at least three different languages).

[fhammerschmidt]

There is now an examples folder with a CSV and some JSON files.