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/ripple/common/MultiSocket.h

@@ -24,8 +24,9 @@
 
 namespace ripple {
 
-/** A Socket that can handshake with multiple protocols. */
-class MultiSocket : public beast::Socket
+/** An abstract_socket that can handshake with multiple protocols. */
+class MultiSocket
+    : public beast::asio::abstract_socket
 {
 public:
     // immutable flags
@@ -101,7 +102,7 @@ public:
         server_proxy = 8
     };
 
-    typedef beast::HandshakeDetectLogicPROXY::ProxyInfo ProxyInfo;
+    typedef beast::asio::HandshakeDetectLogicPROXY::ProxyInfo ProxyInfo;
 
     // Note that this returns the original flags
     virtual Flag getFlags () = 0;