Using Open Source Swift Core Libraries

I sure could use some help getting started with Open Source Swift Core Libraries, specifically URL types and HTTP sessions.

What networking functionality is available in Open Source Swift Core Libraries?

I’ve started the basic Vapor screencasts. However, to do anything useful, I find my server side app needs to fetch some data from other web services. I don’t know where to turn to find documentation on the Core Libraries, where I would expect to find networking features. Are there classes similar to NSURLSession in Swift Core Libraries?

Where would I find documentation on the Core Libraries? I think “The Swift Programming Language - Swift 3.0.1 Edition” only covers the standard Swift library.