Enh/ids only

funpack merge request

Closes #21 (closed)

New --ids_only option, which can be useful when using FUNPACK purely to identify subjects via subject conditional expressions.

Unless the maintainer is being sloppy, this merge request will not be accepted unless the following criteria are met:

[ ] Unit tests pass [ ] Changelog updated [ ] Version number in funpack/__init__.py updated according to Semantic Versioning conventions