sxt: added signature struct;

include/sxt/sxtkey.h

@@ -43,10 +43,16 @@ typedef uint8_t ed25519_signature[ED25519_SIG_LEN];
 typedef struct sxtkey_type {
   uint8_t type;
   uint8_t flags;
-  ed25519_pubkey pubkey;
+  ed25519_pubkey *pubkey;
-  ed25519_privkey privkey;
+  ed25519_privkey *privkey;
+  void *priv;
 } sxtkey_t;
 
+typedef struct sxtsignature_type {
+  uint8_t type;
+  ed25519_signature *sig;
+} sxtsignature_t;
+
 /* ed25519 related functions */
 /** @internal
  * @brief generate an ed25519 key pair