Make it possible to place alp folder elsewhere from workflow root

[benknight]

I tried reorganizing my code recent to make my workflow's logic into a proper Python package, with alp as a subpackage, not too unlike alp's on directory structure. However I ran into an issue where alp expects to be at the workflow's root. You do mention this in the README which is great, and it's probably not a huge refactor to take care of on my own, but I thought this would be a nice improvement to make.