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/context.rs

@@ -60,7 +60,7 @@ impl Context {
     ///
     /// The `isa` argument is currently unused, but the verifier will soon be able to also
     /// check ISA-dependent constraints.
-    pub fn verify<'a>(&self, isa: Option<&TargetIsa>) -> verifier::Result {
+    pub fn verify(&self, isa: Option<&TargetIsa>) -> verifier::Result {
         verifier::verify_context(&self.func, &self.cfg, &self.domtree, isa)
     }