Option to disable/change status line during multiprocessing

[JelleAalbers]

The status line printed during multiprocessing uses sys.stdout.flush() to overwrite the last line in the output, to avoid the screen filling with status messages. However, this means the output becomes difficult to read when it is piped to a logfile. It would be nice to have an option to either disable the status line altogether or have it print a newline instead (but much less frequently).

Related to #376