Refactor beast::asio:

* New tools for completion handlers:
  - wrap_handler provides composed io_service execution guarantees.
  - bind_handler rebinds arguments to handlers.
  - shared_handler type-erases any completion handler.
  - buffer_sequence type-erases templated BufferSequences
  - abstract_socket replaces Socket
  - socket_wrapper replaces SocketWrapper
  - beast::asio placeholders to work with std::bind

* Removed obsolete classes and functions
  - AbstractHandler
  - ComposedAsyncOperation
  - SharedFunction
  - SharedHandler
  - SharedHandlerAllocator
  - SharedHandlerPtr
  - SharedHandlerType
  - SocketBase
  - SocketWrapperStrand
  - wrapHandler

* Refactored classes to use new tools
  - abstract_socket
  - socket_wrapper
  - HandshakeDetector
  - HttpClientType

* Miscellanous tidying
  - socket classes moved to beast::asio namespace
  - beast asio files provide their own namespace declaration.
  - Fix IsCallPossible conflicting template parameter name
  - Use <boost/get_pointer.hpp> for C++11 compatibility.
  - Remove extraneous include path from build environment.

src/beast/modules/beast_asio/async/AsyncObject.h

@@ -20,6 +20,9 @@
 #ifndef BEAST_ASIO_ASYNCOBJECT_H_INCLUDED
 #define BEAST_ASIO_ASYNCOBJECT_H_INCLUDED
 
+namespace beast {
+namespace asio {
+
 /** Mix-in to track when all pending I/O is complete.
     Derived classes must be callable with this signature:
         void asyncHandlersComplete()
@@ -80,4 +83,7 @@ private:
     Atomic <int> m_pending;
 };
 
+}
+}
+
 #endif