Tidy up docs

test/doc/exemplars.cpp

@@ -87,7 +87,7 @@ public:
             body, no more buffers are present.
 
         @li If the optional contains a value, the first element of the
-            pair represents a @b ConstBufferSequence containing one or
+            pair represents a <em>ConstBufferSequence</em> containing one or
             more octets of the body data. The second element indicates
             whether or not there are additional octets of body data.
             A value of `true` means there is more data, and that the

test/doc/http_snippets.cpp

@@ -296,10 +296,10 @@ void fxx() {
 /** Send a message to a stream synchronously.
 
     @param stream The stream to write to. This type must support
-    the @b SyncWriteStream concept.
+    the <em>SyncWriteStream</em> concept.
 
     @param m The message to send. The Body type must support
-    the @b BodyWriter concept.
+    the <em>BodyWriter</em> concept.
 */
 template<
     class SyncWriteStream,