Allow extra files to be added to distinfo directory within the wheel.

[pstradomski]

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That would typically be LICENSE or similar files.

Fixes issue #828.

PR Checklist

Please check if your PR fulfills the following requirements:

• [X] Tests for the changes have been added (for bug fixes / features)
• [X] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• [X] Feature (please, look at the "Scope of the project" section in the README.md file)

What is the current behavior?

Custom files can't be added to dist-info directory in the wheel Issue Number: 828

What is the new behavior?

Allows custom files to be added to dist-info directory in the wheel.

Does this PR introduce a breaking change?

• [ ] Yes
• [X] No

Other information