devel/sem: Add port

sem is a semantic version control tool that works on top of Git. It
parses your code with tree-sitter, extracts every function, class, and
method as an entity, and diffs at the entity level instead of lines.
This means you see "function blahh was modified" instead of "lines x-y
changed."

It works in any Git repo with no setup. It can run as the default
git diff tool; see the WWW for setup instructions.

https://github.com/Ataraxy-Labs/sem
https://ataraxy-labs.github.io/sem