Tidy up use declaration syntax.

lib/entity/src/map.rs

@@ -1,10 +1,12 @@
 //! Densely numbered entity references as mapping keys.
 
+use iter::{Iter, IterMut};
+use keys::Keys;
 use std::marker::PhantomData;
 use std::ops::{Index, IndexMut};
 use std::slice;
 use std::vec::Vec;
-use {EntityRef, Iter, IterMut, Keys};
+use EntityRef;
 
 /// A mapping `K -> V` for densely indexed entity references.
 ///

lib/entity/src/primary.rs

@@ -1,10 +1,12 @@
 //! Densely numbered entity references as mapping keys.
+use iter::{Iter, IterMut};
+use keys::Keys;
 use std::iter::FromIterator;
 use std::marker::PhantomData;
 use std::ops::{Index, IndexMut};
 use std::slice;
 use std::vec::Vec;
-use {EntityRef, Iter, IterMut, Keys};
+use EntityRef;
 
 /// A primary mapping `K -> V` allocating dense entity references.
 ///

lib/entity/src/set.rs

@@ -1,8 +1,9 @@
 //! Densely numbered entity references as set keys.
 
+use keys::Keys;
 use std::marker::PhantomData;
 use std::vec::Vec;
-use {EntityRef, Keys};
+use EntityRef;
 
 /// A set of `K` for densely indexed entity references.
 ///

lib/entity/src/sparse.rs

@@ -7,11 +7,12 @@
 //! > Briggs, Torczon, *An efficient representation for sparse sets*,
 //!   ACM Letters on Programming Languages and Systems, Volume 2, Issue 1-4, March-Dec. 1993.
 
+use map::SecondaryMap;
 use std::mem;
 use std::slice;
 use std::u32;
 use std::vec::Vec;
-use {EntityRef, SecondaryMap};
+use EntityRef;
 
 /// Trait for extracting keys from values stored in a `SparseMap`.
 ///