src,lib: v8-inspector support

This change introduces experimental v8-inspector support. This brings
the DevTools debug protocol allowing Node.js to be debugged with
Chrome DevTools native, or through other debuggers supporting that
protocol.

Partial WebSocket support, to the extent required by DevTools, is
included. This is derived from the implementation in Blink.

v8-inspector support can be disabled by the --without-inspector
configure flag.

PR-URL: https://github.com/nodejs/node/pull/6792


Reviewed-By: jasnell - James M Snell <jasnell@gmail.com>
Reviewed-By: addaleax - Anna Henningsen <anna@addaleax.net>
Reviewed-By: bnoordhuis - Ben Noordhuis <info@bnoordhuis.nl>