- Changed socket output to be based on pipelines
- Changed connection filter glue to be based on pipelines
- Codegen that used `MemoryPoolIterator` for output now uses `WritableBuffer`
- Made `UvWriteReq` async/await friendly with `LibuvAwaitable<T>`
- Deleted MemoryPool and friends
- Replace endpoint configuration via .UseUrls() or --server.urls with Listen*
methods on KestrelSerrverOptions.
- Replace IConnectionFilter with IConnectionAdapter which no longer exposes
ServerAddress via a context.
- Simplify libuv Listener classes
- Support systemd socket activation
- Add docker-based test for systemd socket activation to be run on Travis