Created a pod spec for the new AWS iOS SDK release

It seems like aws made a slight new file structure having the ThirdParty folder needed to be include. Or maybe it is just because it is my first time building a pod spec file I'm totally confused.

Also ran into a problem with a misplaced header file:
-> AWSiOSSDK (1.4.5)
    - ERROR | XCODEBUILD >  AWSiOSSDK/src/Amazon.S3/Model/S3AbortMultiplartUploadsOperation.m:16:9: fatal error: 'S3AbortMultiplartUploadsOperation.h' file not found
So added that explicitly - not sure if this is the right approach ?