Add .idea and .iml to .gitignore

[gfyoung]

These arose when working with the repository in IntelliJ IDE. This is a trivial PR.

[mention-bot]

@gfyoung, thanks for your PR! By analyzing the history of the files in this pull request, we identified @akheron, @zware and @zooba to be potential reviewers.

[the-knights-who-say-ni]

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[gfyoung]

Unfortunately our records indicate you have not signed the CLA.

I signed the CLA two days ago. How long does it take to propagate? Or should I forward the confirmation email to somebody?

[zooba]

Thanks!

[berkerpeksag]

Note that a nearly identical PR (see #6) was rejected before because users can use a global .gitignore file (see also bpo-29510 for Eclipse.)

[gfyoung]

Fair enough, though I think this comment at the end of the PR here suggests that perhaps that that suggestion should be reconsidered. I see no reason to assume that users have a global .gitignore file configured. That's seem to be just asking for accidental file commits.

[berkerpeksag]

Using a global .gitignore file is a best practice. That last comment was about syncing .gitignore with .hgignore.

[gfyoung]

Best practice but not required. Call me cynical, but I don't expect users to do this (in my case, I was working on a machine other than my own and accidentally committed these changes in another PR).