Add _token suffix to token accessors

I think this makes is more clear which things are : AstNode and which
are : AstToken

crates/ra_syntax/src/ast.rs

@@ -287,7 +287,7 @@ where
     let pred = predicates.next().unwrap();
     let mut bounds = pred.type_bound_list().unwrap().bounds();
 
-    assert_eq!("'a", pred.lifetime().unwrap().text());
+    assert_eq!("'a", pred.lifetime_token().unwrap().text());
 
     assert_bound("'b", bounds.next());
     assert_bound("'c", bounds.next());