Refactor header status, reason, and target (API Change):

* header::result is a family of functions to replace header::status

* header interface now uses status enum and also ints

* reason-phrase is no longer stored unless the user explicitly
  requests it.

* When serializing, the standard reason is used for the
  corresponding status code unless the user has changed it.

doc/4_2_message.qbk

@@ -147,8 +147,7 @@ objects:
 ```
     response<string_body> res;
     res.version = 11;   // HTTP/1.1
-    res.status = 200;
-    res.reason("OK");
+    res.result(status::ok);
     res.body = "Hello, world!";
     res.fields.insert("Server", "Beast");
     res.fields.insert("Content-Length", res.body.size());

doc/4_3_streams.qbk

@@ -128,8 +128,7 @@ the number of octets received prior to the server closing the connection:
     {
         response<string_body> res;
         res.version = 11;
-        res.status = 200;
-        res.reason("OK");
+        res.result(status::ok);
         res.fields.insert("Server", "Beast");
         res.body = "Hello, world!";
 

doc/4_4_serializer_streams.qbk

@@ -164,7 +164,7 @@ send_expect_100_continue(
     {
         response<string_body> res;
         read(stream, buffer, res);
-        if(res.status != 100)
+        if(res.result() != status::continue_)
         {
             // The server indicated that it will not
             // accept the request, so skip sending the body.
@@ -229,7 +229,7 @@ send_cgi_response(
     // allowing serialization to use manually provided buffers.
     message<false, buffer_body, fields> res;
 
-    res.status = 200;
+    res.result(status::ok);
     res.version = 11;
     res.fields.insert("Server", "Beast");
     res.fields.insert("Transfer-Encoding", "chunked");

doc/4_5_parser_streams.qbk

@@ -197,8 +197,7 @@ receive_expect_100_continue(
         // send 100 response
         response<empty_body> res;
         res.version = 11;
-        res.status = 100;
-        res.reason("Continue");
+        res.result(status::continue_);
         res.fields.insert("Server", "test");
         write(stream, res, ec);
         if(ec)

doc/4_8_custom_parsers.qbk

@@ -56,7 +56,7 @@ class custom_parser
     /// Called after receiving the start-line (isRequest == false).
     void
     on_response(
-        int status,             // The status-code
+        int code,               // The status-code
         string_view reason,     // The obsolete reason-phrase
         int version,            // The HTTP-version
         error_code& ec);        // The error returned to the caller, if any

doc/6_1_http_message.qbk

@@ -256,13 +256,13 @@ struct header<false, Fields>
     string_view
     reason() const
     {
-        return fields.reason();
+        return fields.reason_impl();
     }
 
     void
     reason(string_view s)
     {
-        fields.reason(s);
+        fields.reason_impl(s);
     }
 
     Fields fields;

doc/quickref.xml

@@ -88,6 +88,7 @@
             <member><link linkend="beast.ref.http__connection">connection</link></member>
             <member><link linkend="beast.ref.http__error">error</link></member>
             <member><link linkend="beast.ref.http__status">status</link></member>
+            <member><link linkend="beast.ref.http__status_class">status_class</link></member>
             <member><link linkend="beast.ref.http__verb">verb</link></member>
           </simplelist>
           <bridgehead renderas="sect3">Type Traits</bridgehead>