Simple C string test

Was added for Javascript, but was not being used in full test-suite.
Rename from javascript_unicode to simple_string and provide for all
languages.
Rewrite to use portable C

Examples/test-suite/string_simple.i

@@ -0,0 +1,13 @@
+%module string_simple
+
+%newobject copy_string;
+
+%inline %{
+#include <string.h>
+const char* copy_string(const char* str) {
+  size_t len = strlen(str);
+  char* newstring = malloc(len + 1);
+  strcpy(newstring, str);
+  return newstring;
+}
+%}