Summary:
So the main Podspec file now has two Subspecs, `Diffing` and for lack of better name `Default`. `Diffing` is purely the files within the common directories (used for Diffing, if in the future we support MacOS NSCollectionView then this may need changing). `Default` depends on `Diffing` but also adds all the non-common files.
To use it via CocoaPods, nothing changes. You `import IGListKit` and you will only have access to the files in the pod you use. (So if you use `IGListKit/Diffing` in your Podfile, then you will only get access to the diffing files). If you do a manual installation, or I assume via Carthage, then you will need to import the correct header file (either `IGListDiffKit.h` or `IGListKit.h` depending on what you want).
Turns out CocoaPods creates it's own umbrella header (unless you tell it otherwise) meaning our ones are unused by it.
Just to confirm `IGListKit` in your Podfile will give you everything, only if you add `/Diffing` will you "opt-out" o
Closes https://github.com/Instagram/IGListKit/pull/368
Differential Revision: D4367438
Pulled By: jessesquires
fbshipit-source-id: 272318ca551e7e8c4177ca3ca501fde23bd9705a
