Make Qei methods fallible

Author: eldruin

src/lib.rs

@@ -974,14 +974,17 @@ pub trait PwmPin {
 // reason: needs to be re-evaluated in the new singletons world. At the very least this needs a
 // reference implementation
 pub trait Qei {
+    /// Enumeration of `Qei` errors
+    type Error;
+
     /// The type of the value returned by `count`
     type Count;
 
     /// Returns the current pulse count of the encoder
-    fn count(&self) -> Self::Count;
+    fn count(&self) -> Result<Self::Count, Self::Error>;
 
     /// Returns the count direction
-    fn direction(&self) -> Direction;
+    fn direction(&self) -> Result<Direction, Self::Error>;
 }
 
 /// Count direction