Update RPCs unopened and ledger for v19 (#28)

Follows nanocurrency/nano-node#2014

docs/commands/rpc-protocol.md

@@ -1382,8 +1382,7 @@ Returns frontier, open block, change representative block, balance, last modifie
   }   
 }
 ```  
-**Optional "representative", "weight", "pending"**
-
+**Optional "representative", "weight", "pending"**  
 Booleans, false by default. Additionally returns representative, voting weight, pending balance for each account   
 
 **Request:**
@@ -1415,16 +1414,18 @@ Booleans, false by default. Additionally returns representative, voting weight,
   }   
 }
 ```  
-**Optional "modified_since"**
-
+**Optional "modified_since"**  
 _version 11.0+_   
 UNIX timestamp (number), 0 by default. Return only accounts modified in local database after specific timestamp   
 
-**Optional "sorting"**
-
+**Optional "sorting"**  
 Boolean, false by default. Additional sorting accounts in descending order  
 NOTE: The "count" option is ignored if "sorting" is specified
 
+**Optional "threshold"**  
+_version 19.0+_  
+Number (128 bit, decimal), default 0. Return only accounts with balance above **threshold**. If **pending** is also given, the number compared with the threshold is the sum of account balance and pending balance.
+
 ---
 
 ### node_id
@@ -2305,6 +2306,9 @@ Returns the total pending balance for unopened accounts in the local database, s
   }   
 ```   
 
+**Optional "threshold"**  
+Number (128 bit, decimal), default 0. Return only accounts with total pending balance above **threshold**.
+
 ---
 
 ### uptime