Merge rust-bitcoin/bitcoin_hashes#153: Add docs to the code create by…

… sha256t_hash_newtype macro

6802b99 Add docs to the code create by sha256t_hash_newtype macro (Tobin C. Harding)

Pull request description:

  When using the `sha256t_hash_newtype` currently no docs are generated,
  this causes lint errors for users who lint for such things.

  Add docs to the new type created by the `sha256t_hash_newtype` macro.

  (This is identical to how we do it in the duplicate macro of the same
  name in `rust-bitcoin`, which can be removed in favour of this one after
  this patch is applied.)

ACKs for top commit:
  apoelstra:
    ACK 6802b99

Tree-SHA512: cfeab98a3c8185b87a0144b36c42b89fd01766dd0e21d8e66652637b9ce3e466009051b538f61d4d033b2a54c0cb6e66607eecbde745dae737003cbf91d86a94

src/sha256t.rs

@@ -143,7 +143,14 @@ impl<T: Tag> HashTrait for Hash<T> {
 #[macro_export]
 macro_rules! sha256t_hash_newtype {
     ($newtype:ident, $tag:ident, $midstate:ident, $midstate_len:expr, $docs:meta, $reverse: expr) => {
-        /// The tag used for [$newtype].
+        sha256t_hash_newtype!($newtype, $tag, $midstate, $midstate_len, $docs, $reverse, stringify!($newtype));
+    };
+
+    ($newtype:ident, $tag:ident, $midstate:ident, $midstate_len:expr, $docs:meta, $reverse: expr, $sname:expr) => {
+        #[doc = "The tag used for ["]
+        #[doc = $sname]
+        #[doc = "]"]
+        #[derive(Copy, Clone, PartialEq, Eq, Default, PartialOrd, Ord, Hash)]
         pub struct $tag;
 
         impl $crate::sha256t::Tag for $tag {