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/sourcemap.rs

@@ -208,7 +208,7 @@ impl MutableSourceMap for SourceMap {
     }
 
     fn def_entity(&mut self, entity: AnyEntity, loc: &Location) -> Result<()> {
-        if self.locations.insert(entity, loc.clone()).is_some() {
+        if self.locations.insert(entity, *loc).is_some() {
             err!(loc, "duplicate entity: {}", entity)
         } else {
             Ok(())