"The scanner" now has a name.
Add missing format string in log message.
Delete confusing log message.

The log says that exitmap exited even though modules might (and probably are)
still running.
Add a statistics class.

It's used throughout exitmap to keep track of scanning statistics.  Before the
program terminates, the statistics are shown.
Correctly terminate and print statistics.

We are able to tell when all circuits are finished by keeping track of all
successful circuits and the "CLOSED" stream events.  Finally, we will print
some scan statistics.
Merge branch 'create_statistics'
Merge branch 'master' of github.com:NullHypothesis/exitmap

Conflicts:
	README.md