musig: rename musig_sort_pubkeys to just sort_pubkeys

This function is useful for Musig but may be useful elsewhere. Rename it
to be more general, and mention it in the Musig docs.

Author: apoelstra

examples/musig.rs

@@ -19,7 +19,7 @@ fn main() {
     let mut pubkeys_ref: Vec<&PublicKey> = pubkeys.iter().collect();
     let pubkeys_ref = pubkeys_ref.as_mut_slice();
 
-    secp.musig_sort_pubkeys(pubkeys_ref);
+    secp.sort_pubkeys(pubkeys_ref);
 
     let mut musig_key_agg_cache = KeyAggCache::new(&secp, pubkeys_ref);
 

src/key.rs

@@ -1620,6 +1620,8 @@ impl<'de> serde::Deserialize<'de> for XOnlyPublicKey {
 impl<C: Verification> Secp256k1<C> {
     /// Sort public keys using lexicographic (of compressed serialization) order.
     ///
+    /// This is the canonical way to sort public keys for use with Musig2.
+    ///
     /// Example:
     ///
     /// ```rust
@@ -1636,10 +1638,10 @@ impl<C: Verification> Secp256k1<C> {
     /// # let mut pubkeys_ref: Vec<&PublicKey> = pubkeys.iter().collect();
     /// # let pubkeys_ref = pubkeys_ref.as_mut_slice();
     /// #
-    /// # secp.musig_sort_pubkeys(pubkeys_ref);
+    /// # secp.sort_pubkeys(pubkeys_ref);
     /// # }
     /// ```
-    pub fn musig_sort_pubkeys(&self, pubkeys: &mut [&PublicKey]) {
+    pub fn sort_pubkeys(&self, pubkeys: &mut [&PublicKey]) {
         let cx = self.ctx().as_ptr();
         unsafe {
             let mut pubkeys_ref = core::slice::from_raw_parts(

src/musig.rs

@@ -281,6 +281,7 @@ impl KeyAggCache {
     /// ensures the same resulting `agg_pk` for the same multiset of pubkeys.
     /// This is useful to do before aggregating pubkeys, such that the order of pubkeys
     /// does not affect the combined public key.
+    /// To do this, call [`Secp256k1::sort_pubkeys`].
     ///
     /// # Returns
     ///