some cursed heuristics for completions, because nvim-cmp kept getting
them wrong. nvim-cmp actually prioritizes kind over sort text, so it
will still get it wrong, but I'm hoping that having a correct sort-text
helps other editors.
Not sure why I didn't test these changes, but the path-join function
didn't actually work fully as expected.
Now, various edge cases have been ironed out:
"/path" + "/foo/bar" -> "/foo/bar", instead of "/path/foo/bar"
"" + "code.fnl" -> "code.fnl", instead of "/code.fnl"
