Better embedding API support (and tests!) for strings with null bytes.

- Test that a foreign method can return strings.
- Test that a foreign method can return a string with null bytes.
- Test wrenCall().
- Allow passing NULL for "v" to wrenCall().
- Allow "a" for passing an explicit length byte array to wrenCall().

src/cli/vm.c

@@ -172,7 +172,7 @@ static void initVM()
 static void freeVM()
 {
   schedulerReleaseMethods();
-
+  
   uv_loop_close(loop);
   free(loop);
 
@@ -259,8 +259,8 @@ uv_loop_t* getLoop()
   return loop;
 }
 
-void setForeignCallbacks(
-    WrenBindForeignMethodFn bindMethod, WrenBindForeignClassFn bindClass)
+void setTestCallbacks(WrenBindForeignMethodFn bindMethod,
+                      WrenBindForeignClassFn bindClass)
 {
   bindMethodFn = bindMethod;
   bindClassFn = bindClass;

src/cli/vm.h

@@ -22,7 +22,7 @@ uv_loop_t* getLoop();
 //
 // Used by the API test executable to let it wire up its own foreign functions.
 // This must be called before calling [createVM()].
-void setForeignCallbacks(WrenBindForeignMethodFn bindMethod,
-                         WrenBindForeignClassFn bindClass);
+void setTestCallbacks(WrenBindForeignMethodFn bindMethod,
+                      WrenBindForeignClassFn bindClass);
 
 #endif