MultifileStream: Added error checking and sensible defaults

get_data crashed violently when no directory was specified,
because the default was empty, a slash was added and the
resulting directory was not writeable. As a consequence,
nullpointeres were followed...

Added some checks, and a check detecting an empty
directory name and use an autogenerated, datetime named
directory instead.
Corrections on argparsing and the verbose flags

Fixed strange and obsolete texts in the help string.

Enabled verbose flag by default (in the future, only
really verbose things should be "verbosed", maybe a
-q quiet flag should be introduced, but probably not
needed anyway...)