finaly add random sietch addr generation

lib/src/lightwallet.rs

@@ -460,6 +460,39 @@ impl LightWallet {
 
         zaddr
     }
+   // Add a new Sietch Addr. This will derive a new zdust address from the seed
+    pub fn add_zaddrdust(&self) -> String {
+        if !self.unlocked {
+            return "".to_string();
+        }
+
+        let pos = self.extsks.read().unwrap().len() as u32;
+      
+         // Use random generator to create a new Sietch seed every time when call.
+       
+         let mut rng = rand::thread_rng();
+         let letter: String = rng.gen_range(b'A', b'Z').to_string();
+         let number: String = rng.gen_range(0, 999999).to_string();
+        // let combi: String = letter.to_string() + number.to_string();
+         let s = format!("{}{:06}", letter, number);
+         //println!("{}", s);
+     
+     let my_string = String::from(s);
+    // let my_immutable_string = &my_string; //This is a &String type
+ let dust: &str = &my_string; //This is an &str type
+
+
+
+     let bip39_seed = bip39::Seed::new(&Mnemonic::from_entropy(&self.seed, Language::English).unwrap(), dust);
+
+     let (_extsk, _extfvk, address) =
+         LightWallet::get_zaddr_from_bip39seed(&self.config, &bip39_seed.as_bytes(), pos);
+
+     let zaddr = encode_payment_address(self.config.hrp_sapling_address(), &address);
+    
+
+     zaddr
+    }
 
     /// Add a new t address to the wallet. This will derive a new address from the seed
     /// at the next position.