Proxy support

Hi - I've added support for using npm-delegate behind a proxy (by using the request library). I've also added no-strictSSL option for dealing with self-signed certificates (because the request lib by default is pretty strict about certs). I've added support for the NODE_DEBUG environment variable for reducing/increasing the output. I've also added tests to cover the changes I've made.

One thing I'm not sure about is the altering of paths to remove/replace "/registry", which just broke things for me so I removed it. If you could explain what the purpose of it was, I can put it back or make it work with registry urls that don't contain '/registry'.

Cheers,
Gareth.