feature: Link to code on GitHub

[andgineer]

Is your feature request related to a problem? Please describe.

For each documented symbol(func, class, etc) optional link to code of that symbol on github.

Describe the solution you'd like

As another option instead of show_code, option github_code_link will add a link to appropriate code on github
like lazydocs doing:
https://andgineer.github.io/aios3/docstrings/stream_iter/

Describe alternatives you've considered

not found

Additional context

none