Automatically make Github releases

[Zethson]

Fixes #27

Approach:

1. Use gh if installed to use the set token cross-platform.
2. Else use PyGithub if installed. Check for GITHUB_TOKEN environment variable which commonly also stores the token.
3. If also not available, ask user for input.
   Fail if neither of the two available.

Tested in a separate repository:

[falexwolf]

Looks great! 😄