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/http/impl/Door.h

@@ -26,7 +26,7 @@ namespace HTTP {
 /** A listening socket. */
 class Door
     : public SharedObject
-    , public AsyncObject <Door>
+    , public beast::asio::AsyncObject <Door>
     , public List <Door>::Node
     , public LeakChecked <Door>
 {

src/ripple/http/impl/Peer.h

@@ -28,12 +28,12 @@ namespace ripple {
 namespace HTTP {
 
 // Holds the copy of buffers being sent
-typedef SharedArg <std::string> SharedBuffer;
+typedef beast::asio::SharedArg <std::string> SharedBuffer;
 
 /** Represents an active connection. */
 class Peer
     : public SharedObject
-    , public AsyncObject <Peer>
+    , public beast::asio::AsyncObject <Peer>
     , public Session
     , public List <Peer>::Node
     , public LeakChecked <Peer>
@@ -229,8 +229,8 @@ public:
 
         if (m_socket->needs_handshake ())
         {
-            m_socket->async_handshake (Socket::server, m_strand.wrap (
-                boost::bind (&Peer::handle_handshake, Ptr(this),
+            m_socket->async_handshake (beast::asio::abstract_socket::server,
+                m_strand.wrap (boost::bind (&Peer::handle_handshake, Ptr(this),
                     boost::asio::placeholders::error,
                         CompletionCounter (this))));
         }

src/ripple/http/impl/Port.cpp

@@ -48,7 +48,7 @@ Port::Port (
     uint16 port_,
     IP::Endpoint const& addr_,
     Security security_,
-    SSLContext* context_)
+    beast::asio::SSLContext* context_)
     : port (port_)
     , addr (addr_)
     , security (security_)