track line numbers between sources and target

[gaborbernat]

Per the PyCon 2019 Typing summit, we agreed that probably the best way to merge stubs and sources is to use this tool. This is needed for mypy issue python/mypy#5028. To be able to use it for that we'll need to preserve/generate sources to output line transformation (so the type checker error reports are not totally off).

I'll work on getting this done, created this issue as a tracker for it and discussion platform.

[gaborbernat]

This project is being retired and archived, so we'll no longer address this.