Use new System.IO.Pipelines API / Project Bedrock#132

Benefits -------- * Pooled memory management reducing allocations. * Instead of current message pump design of pulling/pushing bytes out of a `NetworkStream` and using `CancellationTokenSource`; we can leverage some of the low-level network code that ASP.NET Core is using. * Should allow us to consolidate/delete a lot of code in `SocketWrapper.cs`. * Should help us get the best performance out of the driver from the network when implementing #77. Disadvantages --------------- * Requires **.NET Core 2.1** (I think) References ----------- * ASP.NET Community Standup - May 1, 2018 - SignalR and Project Bedrock with David Fowler https://www.youtube.com/watch?v=ySmUI8O1Rog * Microsoft Build 2018: 1:15 PM | Meet the new stack for real-time web communication: ASP.NET Core SignalR https://www.youtube.com/watch?v=u0_vkWYYXRc https://channel9.msdn.com/Events/Build/2018/BRK2147 * Links: https://blogs.msdn.microsoft.com/dotnet/2018/04/18/performance-improvements-in-net-core-2-1/ https://blog.marcgravell.com/2018/07/pipe-dreams-part-3.html * Related #77