Review & adapt to the new XCS API Docs

[czechboy0]

They're sort of out. Review and adapt some of our API calls (we might not be doing certain things properly).

https://developer.apple.com/library/prerelease/mac/documentation/Xcode/Conceptual/XcodeServerAPIReference/index.html

[cojoj]

I think it'd be nice to start with reviewing the table in README, so we now if they've changed their mind regarding the amount of officially supported things 😬

[czechboy0]

👍