Upgrade & Connect

• Added new API's, dispatch, connect, upgrade.
• Callbacks with error now also receive a { opaque } object as value.
• stream(opts, handler, callback) callback now receive a { trailers, opaque } object as value.
• Misc refactoring and perf improvements.
• Async scope is no longer propagated across events.
• Added idleTimeout option to differentiate timeout of active vs inactive sockets.
• Added support for keep-alive response header timeout hint as well as maxKeepAliveTimeout, keepAliveTimeoutThreshold options.