Add a minimal CLI functionality to urllib.request

[bschubert (Brian Schubert)]

Here’s a few other recent discussions about adding/improving CLIs in stdlib modules:

• Command line interface for the `re` module

• Command-line interface for the `random` module

• Allow `python -m json` to work (in addition to `python -m json.tool`)

• Add `python -m sysconfig --json` option