Harmonize concepts and identifiers with net-ts (API Change):

fix #321

This synchronizes identifier names and some implementation details
with the Networking-TS document and reference implementation.
The following interfaces have changed:

* async_completion
* is_buffer_sequence (removed)
* is_const_buffer_sequence (was is_ConstBufferSequence)
* is_dynamic_buffer (was is_DynamicBuffer)
* is_mutable_buffer_sequence (was is_MutableBufferSequence)
* async_result (new)
* BEAST_HANDLER_TYPE macro (new)
* BEAST_INITFN_RESULT_TYPE macro (new)

Filename changes:

* async_result.hpp (was async_completion.hpp)

doc/quickref.xml

@@ -152,6 +152,7 @@
           <bridgehead renderas="sect3">Classes</bridgehead>
           <simplelist type="vert" columns="1">
             <member><link linkend="beast.ref.async_completion">async_completion</link></member>
+            <member><link linkend="beast.ref.async_result">async_result</link></member>
             <member><link linkend="beast.ref.basic_flat_buffer">basic_flat_buffer</link></member>
             <member><link linkend="beast.ref.basic_multi_buffer">basic_multi_buffer</link></member>
             <member><link linkend="beast.ref.buffers_adapter">buffers_adapter</link></member>
@@ -183,6 +184,11 @@
             <member><link linkend="beast.ref.prepare_buffers">prepare_buffers</link></member>
             <member><link linkend="beast.ref.system_category">system_category</link></member>
           </simplelist>
+          <bridgehead renderas="sect3">Macros</bridgehead>
+          <simplelist type="vert" columns="1">
+            <member><link linkend="beast.ref.BEAST_HANDLER_TYPE">BEAST_HANDLER_TYPE</link></member>
+            <member><link linkend="beast.ref.BEAST_INITFN_RESULT_TYPE">BEAST_INITFN_RESULT_TYPE</link></member>
+          </simplelist>
         </entry>
         <entry valign="top">
           <bridgehead renderas="sect3">Type Traits</bridgehead>
@@ -190,11 +196,10 @@
             <member><link linkend="beast.ref.is_AsyncReadStream">is_AsyncReadStream</link></member>
             <member><link linkend="beast.ref.is_AsyncWriteStream">is_AsyncWriteStream</link></member>
             <member><link linkend="beast.ref.is_AsyncStream">is_AsyncStream</link></member>
-            <member><link linkend="beast.ref.is_BufferSequence">is_BufferSequence</link></member>
             <member><link linkend="beast.ref.is_CompletionHandler">is_CompletionHandler</link></member>
-            <member><link linkend="beast.ref.is_ConstBufferSequence">is_ConstBufferSequence</link></member>
-            <member><link linkend="beast.ref.is_DynamicBuffer">is_DynamicBuffer</link></member>
-            <member><link linkend="beast.ref.is_MutableBufferSequence">is_MutableBufferSequence</link></member>
+            <member><link linkend="beast.ref.is_const_buffer_sequence">is_const_buffer_sequence</link></member>
+            <member><link linkend="beast.ref.is_dynamic_buffer">is_dynamic_buffer</link></member>
+            <member><link linkend="beast.ref.is_mutable_buffer_sequence">is_mutable_buffer_sequence</link></member>
             <member><link linkend="beast.ref.is_SyncReadStream">is_SyncReadStream</link></member>
             <member><link linkend="beast.ref.is_SyncStream">is_SyncStream</link></member>
             <member><link linkend="beast.ref.is_SyncWriteStream">is_SyncWriteStream</link></member>