Move project metadata from setup.cfg to pyproject.toml

[cdce8p]

What do these changes do?

Followup to #639 (comment)

Besides moving the metadata, I also removed the obsolete zip-safe flag.

Metadata diff

 ...
-Maintainer: aiohttp team <[email protected]>
-Maintainer-email: [email protected]
+Maintainer-email: aiohttp team <[email protected]>
-License: Apache-2.0
+License-Expression: Apache-2.0
-Home-page: https://github.com/aio-libs/frozenlist
+Project-URL: Homepage, https://github.com/aio-libs/frozenlist
 ...

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modifications, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep the list in alphabetical order, the file is sorted by name.
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> for example (588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the pr
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files."