closes #80
Conflicts:
	lib/node-http-proxy.js

The number of maxSockets has to be set after the agent is created. Setting the property in the constructor does not work.

This adds a flag to ProxyRequest to disable the setting of x-forwarded-[for|port|proto]
(will change default to true in next commit)

closes issue #72

[api doc test] node-http-proxy now emits `websocket:*` on important WebSocket events. Added tests for these features and updated some code docs