function_view: Add a lightweight span equivalent for functions

Change-Id: I887f844276d618297f9861e64d269dfa4e8062fd
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/function_view.cpp b/src/function_view.cpp
new file mode 100644
index 0000000..a592b7f
--- /dev/null
+++ b/src/function_view.cpp
@@ -0,0 +1 @@
+#include <stdplus/function_view.hpp>