str/cat: Rename from util/string

This still maintains backwards compatability.

Change-Id: Id984a9c2067aaa6986f892c1870834d77b8aec80
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/str/cat.cpp b/src/str/cat.cpp
new file mode 100644
index 0000000..2845a17
--- /dev/null
+++ b/src/str/cat.cpp
@@ -0,0 +1 @@
+#include <stdplus/str/cat.hpp>