Use relative paths in .tufup-repo-config

[dennisvang]

Background

The .tufup-repo-config file, that is created when initializing a repository, includes absolute paths for the keys_dir and repo_dir.

Although these can easily be modified, when necessary, the file should be portable out-of-the-box.

Proposal

It would be more convenient to use relative paths in the .tufup-repo-config file. That is, relative to the config file location.

[wickeat]

This enhancement would be great in making the implementation portable across different environments! Currently, I am manually editing the keys_dir and repo_dir of the .tufup-repo-config file.

[dennisvang]

@wickeat This was a bit tougher than expected. Perhaps you could have a look at #78 to see if the proposed solution would work for your case?

For testing you could do a vcs install, directly from github, e.g.

pip install tufup@git+https://github.com/dennisvang/tufup.git@issue50