Add renumbering of event IDs by default
fix: NOW renumbering is on by default

The previous commit 86e1305 only added the functionality
event_id is now uint32 (instead of int32)
Fix for multiprocessing / HDF5 file writing

The file was somehow not written properly before.
Now the HDF_Worker class (renamed from Worker) also includes
handling of the HDF5 file opening / writing / closing.

This seems to work well so far.