Remove unused and obsolete classes and tidy up:

Many classes required to support type-erasure of handlers and boost::asio
types are now obsolete, so these classes and files are removed:
HTTPClientType, FixedInputBuffer, PeerRole, socket_wrapper,
client_session, basic_url, abstract_socket, buffer_sequence, memory_buffer,
enable_wait_for_async, shared_handler, wrap_handler, streambuf,
ContentBodyBuffer, SSLContext, completion-handler based handshake detectors.
These structural changes are made:
* Some missing includes added to headers
* asio module directory flattened

beast/module/asio/BoostIncludes.h

@@ -0,0 +1,44 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of Beast: https://github.com/vinniefalco/Beast
+    Copyright 2013, Vinnie Falco <vinnie.falco@gmail.com>
+
+    Permission to use, copy, modify, and/or distribute this software for any
+    purpose  with  or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#ifndef BEAST_ASIO_SYSTEM_BOOSTINCLUDES_H_INCLUDED
+#define BEAST_ASIO_SYSTEM_BOOSTINCLUDES_H_INCLUDED
+
+// Make sure we take care of fixing boost::bind oddities first.
+#if !defined(BEAST_CORE_H_INCLUDED)
+#error core.h must be included before including this file
+#endif
+
+// These should have already been set in your project, but
+// if you forgot then we will be optimistic and choose the latest.
+//
+#if BEAST_WIN32
+# ifndef _WIN32_WINNT
+#  pragma message ("Warning: _WIN32_WINNT was not set in your project")
+#  define _WIN32_WINNT 0x0600
+# endif
+# ifndef _VARIADIC_MAX
+#  define _VARIADIC_MAX 10
+# endif
+#endif
+
+// work-around for broken <boost/get_pointer.hpp>
+#include <beast/boost/get_pointer.h>
+
+#endif