add cfail tests

tests/cfail/init.rs

@@ -0,0 +1,18 @@
+#![deny(warnings)]
+#![feature(proc_macro)]
+
+extern crate cortex_m_rtfm as rtfm;
+extern crate stm32f103xx;
+
+use rtfm::app;
+
+app! { //~ error mismatched types
+    device: stm32f103xx,
+}
+
+// ERROR `init` must have signature `fn (init::Peripherals)`
+fn init() {}
+
+fn idle() -> ! {
+    loop {}
+}