Updates and fixes

- Improve and fix SPI HAL and example
- Fix RTIC example

examples/simple/examples/spi.rs

@@ -83,6 +83,8 @@ fn main() -> ! {
         // Can't really verify correct behaviour here. Just verify nothing crazy happens or it hangs up.
         spi0.read(&mut rx_buf[0..2]).unwrap();
 
+        // If the pins are tied together, we should received exactly what we send.
+
         let mut inplace_buf = tx_buf;
         spi0.transfer_in_place(&mut inplace_buf)
             .expect("SPI transfer_in_place failed");