Change JSON serialization example to a generic serialization example

Currently, alternative code is commented out, but this can be useful
when the RDF serialization also works. Maybe this can turn into a
serialization script at some point.

The commit also fixes a typo in the last commit, due to which only one
daily dump was processed instead of all dumps.

In addition, two obsolete methods have been removed from JsonSerializer.
Merge remote-tracking branch 'origin/master' into rdf-serializer