fwd: add a root set of forward decls

CMakeLists.txt

@@ -233,6 +233,8 @@ endif ()
 # Common files
 list (
     APPEND UTIL_FILES
+    fwd.hpp
+
     adapter.hpp
     adapter.cpp
     algo/search.hpp

fwd.hpp

@@ -0,0 +1,5 @@
+#pragma once
+
+namespace cruft {
+    class uri;
+}