Add #![no_std]

enum_derive/src/lib.rs

@@ -183,6 +183,8 @@ assert_eq!(from_troll(&troll_number), Ok(number));
 ```
 */
 
+#![no_std]
+extern crate core as std;
 use std::fmt;
 
 #[doc(hidden)]

newtype_derive/src/lib.rs

@@ -190,6 +190,8 @@ macro_rules! Newtype\2 {
 ```
 */
 
+#![no_std]
+
 mod std_unstable;
 
 #[doc(hidden)]

src/lib.rs

@@ -81,6 +81,8 @@ Third, each derivation macro is expected to result in zero or more items, not in
 Finally, `@impl` is merely a trick to pack multiple, different functions into a single macro.  The sequence has no special meaning; it is simply *distinct* from the usual invocation syntax.
 */
 
+#![no_std]
+
 #[doc(hidden)]
 #[macro_export]
 macro_rules! custom_derive {