`def` can bind multiple vars at once

For example `(def (a b) (10 15))` binds `a` to 10, and `b` to 15

src/pebblisp.c

@@ -14,6 +14,15 @@ Object evalDefArgs(const Object *argForms, struct Environment *env)
     const Object *newSymbol = argForms;
     const char *name = newSymbol->string;
 
+    if(argForms->type == TYPE_LIST && argForms->forward->type == TYPE_LIST) {
+        FOR_POINTERS_IN_LISTS(argForms, argForms->forward) {
+            Object newValue = eval(P2, env);
+            addToEnv(env, P1->string, newValue);
+            cleanObject(&newValue);
+        }
+        return cloneObject(*newSymbol);
+    }
+
     Object newValue = eval(newSymbol->forward, env);
 
     addToEnv(env, name, newValue);