add a `filter` field to rules and modules about peru HOT 5 CLOSED

@olson-sean-k pointed out that "filter" is confusing. E.g. what does this mean:

filter: example.py

Is example.py supposed to in included, or excluded? Who knows. Instead, how about we call this "files"? That seems to work pretty well with all the different ways this attribute can be used:

files: example.py
files:
  - a.py
  - b.py
files: **/test*.py

Also, should we make sure it's an error if we end up matching no files? I feel like it should definitely be an error if you try to add a literal filename that's not there. Git might take care of that for us, actually.

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I think files is a good name for this. I also agree that matching no files should be an error.

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Ok I didn't think this through though: What if the argument to files: is a directory? Do you get everything in that directory? Maybe we should call it paths:? Or glob:? Edit: paths conflicts too closely with plugin fields like path in cp. Sticking with files.

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https://phabricator.buildinspace.com/D30

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675aac2

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