Fix a couple of misses in serde feature

src/lib.rs

@@ -26,7 +26,7 @@
 //!
 //! ###  When not to use
 //! Generally don't use this if your key would have a lot of collisions being represents in 8 bits, otherwise it might be a faster alternative to hash-based maps. You should check yourself before sticking with this crate instead of `std`'s vectorised map implementations.
-#![cfg_attr(not(test), no_std)]
+#![cfg_attr(any(not(test), not(feature = "std")), no_std)]
 #![cfg_attr(nightly, feature(test))] 
 #![cfg_attr(nightly, feature(drain_filter))] 
 #![cfg_attr(nightly, feature(never_type))] 

src/page_impls.rs

@@ -49,7 +49,7 @@ impl<K: hash::Hash, V: hash::Hash> hash::Hash for Page<K,V> {
 #[cfg(feature="serde")]
 const _: () = {
     use serde::*;
-    use std::marker::PhantomData;
+    use core::marker::PhantomData;
     
     impl<K,V> serde::Serialize for Page<K,V>
     where K:Serialize, V: Serialize
@@ -93,7 +93,7 @@ const _: () = {
 		Ok(Page(elems))
 	    } else {
 		use serde::de::Error;
-		Err(A::Error::custom(format!("Expected {} elemts, got {}", MAX, i)))
+		Err(A::Error::custom(alloc::format!("Expected {} elemts, got {}", MAX, i)))
 	    }
 	}
     }