prelude: add HAL prelude module, import embedded-io and embedded-hal …

…traits in prelude

Signed-off-by: Zhouqi Jiang <[email protected]>

allwinner-hal/src/lib.rs

@@ -17,9 +17,17 @@ pub mod smhc;
 pub mod spi;
 #[doc(hidden)]
 pub mod sysctl;
-#[macro_use]
 pub mod uart;
 
+#[doc(hidden)]
+pub mod prelude {
+    pub use embedded_hal::{
+        digital::{InputPin as _, OutputPin as _, StatefulOutputPin as _},
+        spi::SpiBus as _,
+    };
+    pub use embedded_io::{Read as _, Write as _};
+}
+
 #[allow(unused)]
 macro_rules! impl_pins_trait {
     ($(($p: expr, $i: expr, $f: expr): $Trait: ty;)+) => {