🐛 Handle id_required for src-trace

[juiwenchen]

Issues

#23
#15

Summary

Based on the issues, adapt the directive src-trace to have id field, so that the config id_required=True does not block the need generation. This adaptation react to needs config id_from_title and id_length

Implementation

• id is optional and when it's not given, the hash is always generated from titile and project. If directory or file is given, it's taken as well.
• added integration test cases for id_required
• emit error msg when Sphinx-Needs is not set as extensions

[ubmarco]

Can you make this optional, so if users do not provide the ID, you calculate it yourself from the project/directory/file (replace all non-identifier chars with _). Or calculate a short hash from it, just like SN does. Something reproducible with the same inputs.
That ID information will presumably not be helpful because why would people link to the src-trace directive itself?
But if we want src-trace to be a dedicated need, then we should do that. Forcing users to set IDs that will not be useful is meeh.

A src-trace for the same combination of project, directory, and file cannot exist in a Sphinx project because that leads to duplicate needs.

See also #15 (comment)