Fix conversion of Error objects

Convert V8 object with type='error' to DevTools object with
type='object'. This fixes the problem where Error values
were displayed as "undefined" in the front-end.
README: added shell code higlight
Add WebSocketServer error handler.

WebSocketServer emits the errors raised by the underlying http.Server,
thus we have to detect and prevent the situation when a single error
is reported twice.
Fix DebuggerAgent.setVariableValue to object

Fix a bug where object values { objectId: '<id>' } were not correctly
translated to V8 references { handle: <id>}.
RuntimeAgent: implement releaseObject() as no-op
Implement node-debug.

Add a CLI script `node-debug` that:
 1. Runs the supplied script in debug mode
 2. Runs node-inspector.
 3. Opens the user's browser, pointing it at the inspector.

Add a CLI script `run-repl` (used by `node-debug`) that will load
the module in CWD and start a REPL session.
Conversion of object properties as new function