Add module "musig" that implements MuSig2 multi-signatures (BIP 327)

.cirrus.yml

@@ -22,6 +22,7 @@ env:
   RECOVERY: no
   EXTRAKEYS: no
   SCHNORRSIG: no
+  MUSIG: no
   ELLSWIFT: no
   ### test options
   SECP256K1_TEST_ITERS:
@@ -69,6 +70,7 @@ task:
     RECOVERY: yes
     EXTRAKEYS: yes
     SCHNORRSIG: yes
+    MUSIG: yes
     ELLSWIFT: yes
   matrix:
      # Currently only gcc-snapshot, the other compilers are tested on GHA with QEMU
@@ -86,6 +88,7 @@ task:
     RECOVERY: yes
     EXTRAKEYS: yes
     SCHNORRSIG: yes
+    MUSIG: yes
     ELLSWIFT: yes
     WRAPPER_CMD: 'valgrind --error-exitcode=42'
     SECP256K1_TEST_ITERS: 2