bpo-39452: Improve the __main__ module documentation

[geryogam]

This PR will apply the following changes on the __main__ module documentation:

• replace an incorrect use of "script" with "code";
• replace incorrect and inconsistent uses of "scope" with "environment";
• add missing cases where the __main__ module is also initialized (when using the -c and -m arguments);
• replace the ambiguous "when it is imported" by "not initialized from an import statement" since using a -m argument also performs import for instance;
• add missing cases for the conditional execution of the if body (all the cases when the module is not initialized from an import statement);
• make the if block comment PEP 8-compliant (capital initialised, period ended);
• add a missing case for the conditional execution of the __main__.py submodule of a package (when the package is initialized from a file argument).

https://bugs.python.org/issue39452

[mangrisano]

LGTM.

[mariatta-bot]

🤖 Mariatta was mentioned, but she's out of open source until end of September 2019. Hopefully someone else can look into this in the meantime.

[csabella]

@maggyero, please open a bug tracker ticket for this. That will provide the chance for more people to see the change and comment on it. Thanks!

[geryogam]

Done @csabella.

[terryjreedy]

To me, at least the first two changes in the description are wrong. See the issue for discussion.

[bedevere-bot]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[geryogam]

I have made the requested changes; please review again.

[bedevere-bot]

Thanks for making the requested changes!

@terryjreedy: please review the changes made to this pull request.

[terryjreedy]

Remove trailing whitespace with patchcheck, as mentioned in devguide.

[terryjreedy]

@stevendaprano Changes were made in response to your review on the issue.

[geryogam]

@terryjreedy

Remove trailing whitespace with patchcheck, as mentioned in devguide.

Done.

[ambv]

Closing in favor of GH-26883.