## Summary
I don't know if this is actually a good change, but it tries to make the
editable install experience more consistent. Specifically, we now
support...
```
# Use a relative path with a `file://` prefix.
# Prior to this PR, we supported `file:../foo`, but not `file://../foo`, which felt inconsistent.
-e file://../foo
# Use environment variables with paths, not just URLs.
# Prior to this PR, we supported `file://${PROJECT_ROOT}/../foo`, but not the below.
-e ${PROJECT_ROOT}/../foo
```
Importantly, `-e file://../foo` is actually not supported by pip... `-e
file:../foo` _is_ supported though. We support both, as of this PR. Open
to feedback.
Charlie Marsh