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/result.rs

@@ -3,7 +3,6 @@
 use verifier;
 use std::error::Error as StdError;
 use std::fmt;
-use std::result;
 
 /// A compilation error.
 ///
@@ -32,7 +31,7 @@ pub enum CtonError {
 }
 
 /// A Cretonne compilation result.
-pub type CtonResult = result::Result<(), CtonError>;
+pub type CtonResult = Result<(), CtonError>;
 
 impl fmt::Display for CtonError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {