Add an async demonstration

Cargo.toml

@@ -24,3 +24,6 @@ spin = { git = "https://github.com/bspeice/spin-rs.git" }
 thread-id = "3.3"
 
 qadapt-macro = { version = "0.7.1", path = "./qadapt-macro" }
+
+[dev-dependencies]
+futures = "0.1"

tests/async.rs

@@ -0,0 +1,33 @@
+use futures::future::ok;
+use futures::prelude::*;
+use qadapt::assert_no_alloc;
+use qadapt::no_alloc;
+use qadapt::QADAPT;
+
+#[global_allocator]
+static Q: QADAPT = QADAPT;
+
+#[no_alloc]
+fn async_box() -> impl Future<Item = Box<u8>, Error = ()> {
+    ok(12).and_then(|e| Ok(Box::new(e)))
+}
+
+#[test]
+fn raw_call() {
+    async_box();
+}
+
+#[test]
+fn guarded_call() {
+    assert_no_alloc!(async_box());
+}
+
+#[test]
+#[should_panic]
+fn guarded_poll() {
+    if cfg!(debug_assertions) {
+        assert_no_alloc!(async_box().poll().unwrap());
+    } else {
+        panic!("Intentional")
+    }
+}