Lint fixes (#99)

* Replace a single-character string literal with a character literal.

* Use is_some() instead of comparing with Some(_).

* Add code-quotes around type names in comments.

* Use !...is_empty() instead of len() != 0.

* Tidy up redundant returns.

* Remove redundant .clone() calls.

* Remove unnecessary explicit lifetime parameters.

* Tidy up unnecessary '&'s.

* Add parens to make operator precedence explicit.

* Use debug_assert_eq instead of debug_assert with ==.

* Replace a &Vec argument with a &[...].

* Replace `a = a op b` with `a op= b`.

* Avoid unnecessary closures.

* Avoid .iter() and .iter_mut() for iterating over containers.

* Remove unneeded qualification.

lib/cretonne/src/ir/valueloc.rs

@@ -98,16 +98,16 @@ impl Default for ArgumentLoc {
 impl ArgumentLoc {
     /// Is this an assigned location? (That is, not `Unassigned`).
     pub fn is_assigned(&self) -> bool {
-        match self {
-            &ArgumentLoc::Unassigned => false,
+        match *self {
+            ArgumentLoc::Unassigned => false,
             _ => true,
         }
     }
 
     /// Is this a register location?
     pub fn is_reg(&self) -> bool {
-        match self {
-            &ArgumentLoc::Reg(_) => true,
+        match *self {
+            ArgumentLoc::Reg(_) => true,
             _ => false,
         }
     }