Make arena mod public

Author: maciejhirsz

src/arena.rs

@@ -1,3 +1,6 @@
+//! Module containing the `Arena` and `Uninitialized` structs. For convenience the
+//! `Arena` is exported at the root of the crate.
+
 use std::mem::size_of;
 use std::cell::Cell;
 

src/lib.rs

@@ -96,7 +96,7 @@ pub mod cell;
 pub mod map;
 pub mod set;
 pub mod list;
-mod arena;
+pub mod arena;
 mod bloom;
 mod impl_partial_eq;
 mod impl_debug;