docs: point pybgl links to Bitgesell repository

[tolga-tom-nook]

Summary

• Updates README/install docs/Sphinx GitHub metadata to point to the current BitgesellOfficial/pybgl repository.
• Replaces stale bitaps-com/pybgl clone, issue tracker, and package URL references with the canonical Bitgesell repo.

Validation

• python3 -m compileall -q pybgl
• stale-link scan for bitaps-com/pybgl in README/setup/docs returned no matches
• git diff --check

Bounty context: submitted for the Bitgesell improvement/PR bounty program (#81 / #39). If accepted, payout address: 0x4a76c7E64C08cF29B59eFC640b4ada97A270d428 (EVM/USDT-compatible).

[MyTH-zyxeon]

Review assist for maintainers:

This looks like a narrow docs/metadata retarget from the legacy bitaps-com host to the current BitgesellOfficial pybgl repository. I checked the patch scope: README install instructions, Sphinx GitHub banner metadata, docs source/index links, docs installation clone URL, and setup.py package URL all move to the official org without changing runtime code.

Suggested merge checks:

• Search the touched docs/package metadata for bitaps-com/pybgl and confirm no stale project URL remains in those files.
• Build the Sphinx docs, or at least render the index/install pages, so the new GitHub link target and HTTPS clone snippets display correctly.
• Inspect package metadata after setup.py parsing to confirm the PyPI/project URL now points at https://github.com/BitgesellOfficial/pybgl.

I do not see a code-path or dependency risk in this patch as written; the main acceptance criterion is that generated docs/package metadata stop sending users to the old repository.