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/jumptable.rs

@@ -65,7 +65,7 @@ impl JumpTableData {
     /// Enumerate over all `(idx, dest)` pairs in the table in order.
     ///
     /// This returns an iterator that skips any empty slots in the table.
-    pub fn entries<'a>(&'a self) -> Entries {
+    pub fn entries(&self) -> Entries {
         Entries(self.table.iter().cloned().enumerate())
     }