0.5.6 cosmetics and versions upgrade, JVM target to 11 for better android compatibility

src/commonMain/kotlin/net/sergeych/crypto2/PBKD.kt

@@ -91,9 +91,9 @@ object PBKD {
 
     /**
      * Binary id is a binary hash-capable key, we use it. byte array can't be a hash key in kotlin: its value
-     * does not depend on the byte content.
+     * does not depend on the byte content. It is unsafe to use it outside the generator!
      */
-    fun key(kdf: KDF, password: String): BinaryId =
+    private fun key(kdf: KDF, password: String): BinaryId =
         BinaryId.createFromBytes(
             0,
             BipackEncoder.encode(kdf) + blake2b3l(password.encodeToUByteArray()).asByteArray()