Add lambda demonstration to Jai example

Author: rexim

examples/counter.jai

@@ -7,7 +7,7 @@ coroutine_wake_up :: (id: int) #foreign coroutine;
 coroutine_init :: () #foreign coroutine;
 coroutine_finish :: () #foreign coroutine;
 coroutine_yield :: () #foreign coroutine;
-coroutine_go :: (f: (*void) #c_call, arg: *void) #foreign coroutine;
+coroutine_go :: (f: (*void) #c_call, arg: *void = null) #foreign coroutine;
 coroutine_id :: () -> int #foreign coroutine;
 coroutine_alive :: () -> int #foreign coroutine;
 
@@ -24,6 +24,11 @@ counter :: (arg: *void) #c_call {
 main :: () {
     coroutine_init();
     defer coroutine_finish();
+    coroutine_go((arg: *void) #c_call {
+        push_context {
+            print("[%] Hello from Jai Lambda\n", coroutine_id());
+        }
+    });
     coroutine_go(counter, cast(*void) 5);
     coroutine_go(counter, cast(*void) 10);
     while coroutine_alive() > 1 {