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/reader/src/parser.rs

@@ -282,7 +282,7 @@ impl<'a> Parser<'a> {
                 None => break,
             }
         }
-        return self.lookahead;
+        self.lookahead
     }
 
     // Begin gathering comments associated with `entity`.
@@ -397,7 +397,7 @@ impl<'a> Parser<'a> {
 
     fn error(&self, message: &str) -> Error {
         Error {
-            location: self.loc.clone(),
+            location: self.loc,
             message: message.to_string(),
         }
     }
@@ -1066,7 +1066,7 @@ impl<'a> Parser<'a> {
                     self.consume();
                     self.parse_instruction(results, encoding, result_locations, ctx, ebb)?;
                 }
-                _ if results.len() != 0 => return err!(self.loc, "expected -> or ="),
+                _ if !results.is_empty() => return err!(self.loc, "expected -> or ="),
                 _ => self.parse_instruction(results, encoding, result_locations, ctx, ebb)?,
             }
         }