Rename heap modules in the core, alloc, and std crates to alloc

src/libstd/lib.rs

@@ -477,7 +477,11 @@ pub mod path;
 pub mod process;
 pub mod sync;
 pub mod time;
-pub mod heap;
+pub mod alloc;
+
+#[unstable(feature = "allocator_api", issue = "32838")]
+#[rustc_deprecated(since = "1.27.0", reason = "module renamed to `alloc`")]
+pub use alloc as heap;
 
 // Platform-abstraction modules
 #[macro_use]