Parallelized using multiprocessing library. I'm not really sure about
the code being thread safe. I think we don't care if tweets are appended
to the files in a different order, but the metadata files being
corrupted would be problematic. In the first tests the metadata were
fine, but I think this line is probably not thread safe (two threads
could load try to update the old value at the same time, resulting in
inconsistencies):

"""
metadata_file["files"][file_path]["count"] += increase
"""

Apart from that, code is much faster than before.

Simpler, more elegant and slightly faster version using the cursors instead of building a list of tweets for each page

Repository contains just one simple script for the moment to dump the
"tweets" collection of a Mongo database to a JSON file in a
"pymongodump" directory that is created at the moment and place of
execution.
Faster than mongoexport, although the format of the resulting JSONs is
somewhat different (adapted to Python's syntax).