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/HTTPHeaders.cpp

@@ -0,0 +1,108 @@
+//------------------------------------------------------------------------------
+/*
+    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/HTTPHeaders.h>
+#include <algorithm>
+
+namespace beast {
+
+HTTPHeaders::HTTPHeaders ()
+{
+}
+
+HTTPHeaders::HTTPHeaders (StringPairArray& fields)
+{
+    m_fields.swapWith (fields);
+}
+
+HTTPHeaders::HTTPHeaders (StringPairArray const& fields)
+    : m_fields (fields)
+{
+}
+
+HTTPHeaders::HTTPHeaders (HTTPHeaders const& other)
+    : m_fields (other.m_fields)
+{
+}
+
+HTTPHeaders& HTTPHeaders::operator= (HTTPHeaders const& other)
+{
+    m_fields = other.m_fields;
+    return *this;
+}
+
+bool HTTPHeaders::empty () const
+{
+    return m_fields.size () == 0;
+}
+
+std::size_t HTTPHeaders::size () const
+{
+    return m_fields.size ();
+}
+
+HTTPField HTTPHeaders::at (int index) const
+{
+    return HTTPField (m_fields.getAllKeys () [index],
+                      m_fields.getAllValues () [index]);
+}
+
+HTTPField HTTPHeaders::operator[] (int index) const
+{
+    return at (index);
+}
+
+String HTTPHeaders::get (String const& field) const
+{
+    return m_fields [field];
+}
+
+String HTTPHeaders::operator[] (String const& field) const
+{
+    return get (field);
+}
+
+String HTTPHeaders::toString () const
+{
+    String s;
+    for (int i = 0; i < m_fields.size (); ++i)
+    {
+        HTTPField const field (at(i));
+        s << field.name() << ": " << field.value() << newLine;
+    }
+    return s;
+}
+
+std::map <std::string, std::string>
+HTTPHeaders::build_map() const
+{
+    std::map <std::string, std::string> c;
+    auto const& k (m_fields.getAllKeys());
+    auto const& v (m_fields.getAllValues());
+    for (std::size_t i = 0; i < m_fields.size(); ++i)
+    {
+        auto key (k[i].toStdString());
+        auto const value (v[i].toStdString());
+        std::transform (key.begin(), key.end(), key.begin(), ::tolower);
+        c[key] = value;
+    }
+    return c;
+}
+
+}