Speed up the second stage of the report generation

Speed up the second stage of the report generation

A lot of temporary files are produced after the log is split into several
files each containing the data of the users but those temporary files were
constantly being opened and closed for each line to be written into. It
was a small waste of time.

The new processing opens the temporary user's files once per user, process
the data of the corresponding user and generate the temporary file with
those data. The gain is roughly 10% on my data set.