Update to rustfmt-preview (#348)

* Update to rustfmt-preview.

* Run "cargo fmt --all" with rustfmt 0.4.1.

rustfmt 0.4.1 is the latest release of rustfmt-preview available on the
stable channel.

* Fix a long line that rustfmt 0.4.1 can't handle.

* Remove unneeded commas left behind by rustfmt.

lib/codegen/src/dbg.rs

@@ -126,7 +126,7 @@ macro_rules! dbg {
 #[cfg(not(feature = "std"))]
 #[macro_export]
 macro_rules! dbg {
-    ($($arg:tt)+) => {}
+    ($($arg:tt)+) => {};
 }
 
 /// Helper for printing lists.