Incremented the number of events manageable by the event loop.
Dispatch EPOLLRDHUP first.
Fixed invalid pointer dereference.
Keep-Alive support.

* Added HTTPRequestQueue class.
* Changed the HTTPRequest interface to have two separate buffers,
  one for the headers and one for the body. This way the headers
  are copied all together in one shot from the receive buffer,
  and in future will be possible to implement particular policies
  for the body storage (for example with some heuristic based on the
  content-length).
* Adapted the HTTPConnection class to use the new HTTPRequestQueue
  class.
Missed header.
Merge branch 'feature/keep-alive' into develop