Add async RPC queue and operation classes.

Add z_getoperationstatus RPC command.
Add z_sendmany RPC command (dummy implementation, does not send actual
coins).

src/asyncrpcqueue.h

@@ -0,0 +1,61 @@
+// Copyright (c) 2014 The Zcash developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef ASYNCRPCQUEUE_H
+#define ASYNCRPCQUEUE_H
+
+#include "asyncrpcoperation.h"
+
+#include <iostream>
+#include <string>
+#include <chrono>
+#include <queue>
+#include <unordered_map>
+#include <vector>
+#include <future>
+#include <thread>
+#include <utility>
+
+#include <memory>
+
+
+typedef std::unordered_map<AsyncRPCOperationId, std::shared_ptr<AsyncRPCOperation> > AsyncRPCOperationMap; 
+
+
+class AsyncRPCQueue {
+public:
+    AsyncRPCQueue();
+    virtual ~AsyncRPCQueue();
+
+    // We don't want queue to be copied or moved around
+    AsyncRPCQueue(AsyncRPCQueue const&) = delete;             // Copy construct
+    AsyncRPCQueue(AsyncRPCQueue&&) = delete;                  // Move construct
+    AsyncRPCQueue& operator=(AsyncRPCQueue const&) = delete;  // Copy assign
+    AsyncRPCQueue& operator=(AsyncRPCQueue &&) = delete;      // Move assign
+
+    void addWorker();
+    int getNumberOfWorkers();
+    bool isClosed();
+    void close();
+    void cancelAllOperations();
+    int getOperationCount();
+    std::shared_ptr<AsyncRPCOperation> getOperationForId(AsyncRPCOperationId);
+    std::shared_ptr<AsyncRPCOperation> popOperationForId(AsyncRPCOperationId);
+    void addOperation(const std::shared_ptr<AsyncRPCOperation> &ptrOperation);
+
+private:
+    // addWorker() will spawn a new thread on this method
+    void run(int workerId);
+
+    std::mutex cs_lock;
+    std::condition_variable cs_condition;
+    bool closed;
+    AsyncRPCOperationMap operationMap;
+    std::queue <AsyncRPCOperationId> operationIdQueue;
+    std::vector<std::thread> workers;
+};
+
+#endif
+
+