Tidy up core sources:

The core headers are moved to their own directory (but remain in
the same namespace).

examples/http_async_server.hpp

@@ -23,7 +23,7 @@
 #include "file_body.hpp"
 #include "http_stream.hpp"
 
-#include <beast/placeholders.hpp>
+#include <beast/core/placeholders.hpp>
 #include <boost/asio.hpp>
 #include <cstdio>
 #include <iostream>

examples/http_stream.hpp

@@ -20,9 +20,9 @@
 #ifndef BEAST_HTTP_STREAM_H_INCLUDED
 #define BEAST_HTTP_STREAM_H_INCLUDED
 
+#include <beast/core/async_completion.hpp>
+#include <beast/core/basic_streambuf.hpp>
 #include <beast/http.hpp>
-#include <beast/async_completion.hpp>
-#include <beast/basic_streambuf.hpp>
 #include <boost/asio/io_service.hpp>
 #include <boost/intrusive/list.hpp>
 #include <memory>
@@ -234,7 +234,7 @@ public:
         error_code ec;
         cancel(ec);
         if(ec)
-            throw boost::system::system_error{ec};
+            throw system_error{ec};
     }
 
     /** Cancel pending operations.
@@ -273,7 +273,7 @@ public:
         error_code ec;
         read(msg, ec);
         if(ec)
-            throw boost::system::system_error{ec};
+            throw system_error{ec};
     }
 
     /** Read a HTTP message from the stream.
@@ -370,7 +370,7 @@ public:
         error_code ec;
         write(msg, ec);
         if(ec)
-            throw boost::system::system_error{ec};
+            throw system_error{ec};
     }
 
     /** Write a HTTP message to the stream.

examples/http_stream.ipp

@@ -20,11 +20,11 @@
 #ifndef BEAST_HTTP_STREAM_IPP_INCLUDED
 #define BEAST_HTTP_STREAM_IPP_INCLUDED
 
+#include <beast/core/bind_handler.hpp>
+#include <beast/core/handler_alloc.hpp>
 #include <beast/http/message_v1.hpp>
 #include <beast/http/read.hpp>
 #include <beast/http/write.hpp>
-#include <beast/bind_handler.hpp>
-#include <beast/handler_alloc.hpp>
 #include <cassert>
 
 namespace beast {

examples/websocket_example.cpp

@@ -5,7 +5,7 @@
 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 //
 
-#include <beast/to_string.hpp>
+#include <beast/core/to_string.hpp>
 #include <beast/websocket.hpp>
 #include <boost/asio.hpp>
 #include <iostream>