Offer python -m sqlite_utils as an alternative to sqlite-utils

[simonw]

Add this to sqlite_utils/cli.py:

if __name__ == "__main__":
    cli()

Now the tool can be run using python -m sqlite_utils.cli --help

Originally posted by @simonw in #364 (comment)

[simonw]

Even better, inspired by rich, support python -m sqlite_utils. https://github.com/Textualize/rich/blob/master/rich/__main__.py

[simonw]

Test failure on Python 3.6:

E TypeError: __init__() got an unexpected keyword argument 'capture_output'

[simonw]

In Python 3.6: https://docs.python.org/3.6/library/subprocess.html

This does not capture stdout or stderr by default. To do so, pass PIPE for the stdout and/or stderr arguments.