Add HTTP client proxy support

[zcourts]

Implement proxy support such that GET and POST requests directly write request contents to the proxy when using http without the upgrade header.

For any other HTTP method i.e. PUT, DELETE or when using SSL or WebSocket proxy using the HTTP connect method, ala HTTP tunneling.

Regardless of the proxy method, add support for HTTP Basic authentication.

Note to self: Remember to use keep alive with:
Proxy-Connection: keep-alive
Connection: keep-alive
for web sockets

RFCs:

Upgrading to TLS
http://tools.ietf.org/html/rfc2817#section-5.2 in HTTP 1.1

HTTP 1.1 spec
http://tools.ietf.org/html/rfc2068#section-8.1.3

[zcourts]

Pseudo logic

If proxy enabled
   if !SSL and (GET or POST)
     connect to proxy host:port and write HTTP request with Proxy-Authorization [if provided]
   else
      connect to proxy host:port
      write HTTP connect request with Proxy-Authorization [if provided]
      write original request to established TCP stream for the proxy to forward
   end if
end if

[zcourts]

added in 0.0.7
Latest version at http://search.maven.org/#browse%7C-819925117