Use "logging" instead of "print" to enable output-control

[exhuma]

Currently proselint writes non-essential information onto stout. This is caused by using the print() function for those messages. For example, the following message

Using in-memory shelf for cache file /home/users/malbert/.cache/proselint/checks.airlinese.misc.check

is cause by

proselint/proselint/tools.py

Line 81 in ea8c574

print('Using in-memory shelf for cache file %s' % cachepath)

This makes proselint excessively verbose on large projects and there is no way to circumvent this.

On typical CLI applications it is possible to redirect stderr somewhere else, for example I would expect to be able to do this:

proselint my_file.rst 2>/dev.null

to get only the important messages. Even better, I would expect to use something like a -q/--quiet flag instead.

By using the logging framework in Python the first point is automatic because log-messages are written by default to stderr.
The "quiet" flag is then also trivial to implement as one could just increase the log-level, for example:

if quiet:
    logging.getLogger().setLevel(logging.ERROR)

As it is now, I am forced to run proselint through a couple of negative grep calls to filter out everything I don't want to see. This is cumbersome, error prone and risks accidentally filtering out too much.

By having a "quiet" flag (or simply using logging and thus writing to stderr) would make this a lot easier and make the output much more readable.