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/HTTPField.cpp

@@ -0,0 +1,57 @@
+//------------------------------------------------------------------------------
+/*
+    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.
+*/
+//==============================================================================
+
+#include <beast/module/asio/HTTPField.h>
+
+namespace beast {
+
+HTTPField::HTTPField ()
+{
+}
+
+HTTPField::HTTPField (String name_, String value_)
+    : m_name (name_)
+    , m_value (value_)
+{
+}
+
+HTTPField::HTTPField (HTTPField const& other)
+    : m_name (other.m_name)
+    , m_value (other.m_value)
+{
+}
+
+HTTPField& HTTPField::operator= (HTTPField const& other)
+{
+    m_name = other.m_name;
+    m_value = other.m_value;
+    return *this;
+}
+
+String HTTPField::name () const
+{
+    return m_name;
+}
+
+String HTTPField::value () const
+{
+    return m_value;
+}
+
+}