Example scripts: find all entities, read all books

[macfreek]

@mfld-fr Could you review these? The first is an older script (2017 or 2018), the second relative new (late 2018).

Note to self: I first must add a test that runs these scripts before approving the merge request.

[mfld-fr]

Any working example as such ones is good to have. I would just advise to avoid accumulating examples just for the satisfaction of having the biggest collection. Added value of examples is that they help to understand the library API or some tricky points of the MC world format, and they inspire ideas for more applications. So up to you as the maintainer to decide if these examples are meaningful or not...