Add experimental icy_stream Shoutcast stream filter:

fix #595, fix #1151

This provides a stream filter which converts the ICY HTTP
response handshake at the beginning of a stream to HTTP/1.1.

test/beast/experimental/flat_stream.cpp

@@ -103,7 +103,7 @@ public:
     }
 };
 
-BEAST_DEFINE_TESTSUITE(beast,example,flat_stream);
+BEAST_DEFINE_TESTSUITE(beast,core,flat_stream);
 
 } // beast
 } // boost