nginx refactoring

This branch contains experimental code. do not use in production yet.

Refactoring on the nginx module, including:
 - Better handling larger posts;
 - Now using nginx echo module during the regression tests.
 - Better interacting with neginx chain rules
 - Separation of the request handling and content filters.
 - Better handling nginx sessions and resource counts to allow a
   more efficient garbage collector.
 - Handling both http/1.0 and 1.1, including keep-alive.
 - Tests are now capable to test nginx as a proxy or end-server.
 - Tested agains nginx 1.6 and 1.7.