Add an iterators module with extra Iterator methods.

Start with an adjacent_pairs() iterator adapter.

lib/cretonne/src/lib.rs

@@ -14,10 +14,10 @@ pub const VERSION: &'static str = env!("CARGO_PKG_VERSION");
 pub mod dbg;
 
 pub mod binemit;
-pub mod flowgraph;
 pub mod dominator_tree;
 pub mod entity_list;
 pub mod entity_map;
+pub mod flowgraph;
 pub mod ir;
 pub mod isa;
 pub mod regalloc;
@@ -28,6 +28,7 @@ pub mod verifier;
 mod abi;
 mod constant_hash;
 mod context;
+mod iterators;
 mod legalizer;
 mod packed_option;
 mod partition_slice;