separate lib from middleware about polyfill-middleware

[defunctzombie]

I agree. I kinda think the polyfill creating portion could exist in the base polyfill lib. Tho there are actually some opinions with that because you could technically write something that uses streams during polyfill source bundling and sends that to the end user.

So for now I went with just having it here as a starting point. I tried to separate out logically to make that transition easier later.

[jonathanong]

well that's just an optimization. i doubt it'll be worth using streams though since this is pretty small and you could just store it in memory.

+1 to including it in the lib though - was going to add that but what you wrote sounded like the opposite so i was like nvm... haha