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.

modules/beast_asio/tests/PeerTest.cpp

@@ -17,6 +17,9 @@
 */
 //==============================================================================
 
+namespace beast {
+namespace asio {
+
 PeerTest::Result::Result ()
     : m_ec (TestPeerBasics::make_error (TestPeerBasics::errc::skipped))
     , m_message (m_ec.message ())
@@ -98,3 +101,6 @@ bool PeerTest::Results::report (UnitTest& test, bool beginTestCase) const
         success = false;
     return success;
 }
+
+}
+}