Improves Kestrel to reject requests that don't conform to HTTP spec.
RFC 7230 section 5.4: "A server MUST respond with a 400 (Bad Request)
status code to any HTTP/1.1 request message that lacks a Host header
field and to any request message that contains more than one Host
header field or a Host header field with an invalid field-value."
See https://tools.ietf.org/html/rfc7230#section-5.4.
Other changes:
- update VS code settings to work better with CLI 2.0
- update tests that were subject to infinite hangs
- 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