Slight optimisation of status_code functions

Fixes #143: Content-Length is now initialized to 0

Removed unused lambda captures in examples

compile clean with gcc 4.6.3

Updated features in README.md

Examples: fixed crash in default_resource

Fixes #28

Response stream now subclass std::ostream. Also some cleanup of defau…

…lt_resource example.

Update README.md

renamed #define CLIENT_WS_HPP and CLIENT_WSS_HPP to CLIENT_HTTP_HPP a…

…nd CLIENT_HTTPS_HPP.