Add a benchmark to test the Wren C API.

I've got some ideas on how to tweak the embedding API, but I want to
see what performance impact they have first, so this adds a little
benchmark that just calls a foreign method a ton of times.

test/api/call.wren

@@ -1,4 +1,4 @@
-class Api {
+class Call {
   static noParams {
     System.print("noParams")
   }