Stop using deprecated cgi module

Summary:
The cgi module has been deprecated and will be removed in Python 3.13.

Side edits:

• adhere more to Python conventions
• improve HTML doctype
• proofread messages

Source: https://github.com/simon-budig/woof/pull/21

Ref T2041.

Test Plan:

• woof CONTRIBUTORS.md
• woof archiv/
• woof -U (without upload)
• woof -U, then compare file hashes

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T2041

Differential Revision: https://devcentral.nasqueron.org/D3536