Have Natalie be smart about targets in xcodeproj #64
Description
One feature request I'd like is for Natalie to allow an xcodeproj file as argument, parse it to find out which storyboards are included in which targets and generate a Storyboards.swift for each target. Like that, if the project has storyboards in an app target and in an extension target, Natalie will generate a separate file to include in each target that only makes the targets storyboards visible. It will also solve name collisions when targets have storyboards with the same name.
As a side note, I'm currently implementing this by wrapping Natalie around a ruby script which parses an xcodeproj file with the Xcodeproj gem (which came out of the Cocoapods project) and feeds Storyboard files to natalie. Unfortunately, there doesn't seem to be equally good Xcodeproj parsing libs in Swift.