fix(logging): don't write to stderr when used as a library

[zed]

Let applications that use peewee_migrate to control their output. https://docs.python.org/3/library/logging.handlers.html#nullhandler

Fixes #216

Note: the code just expresses the intent to start the discussion. It may need to be tweaked before the merge.

cc/ @klen

[klen]

@zed Thank you!