modbus worker (#399)

* link TCP port with existing socket

* add linkTelnet

* add linkTcpRTUBuffered

* worker api

apis/worker.js

@@ -0,0 +1,31 @@
+const Worker = require("../worker/index");
+
+module.exports = function(Modbus) {
+    const cl = Modbus.prototype;
+
+
+    cl.setWorkerOptions = function(options) {
+        if (this._worker) {
+            this._worker.setOptions(options);
+        } else {
+            this._worker = new Worker(this, options);
+        }
+    };
+
+    cl.send = function(request) {
+        if(!this._worker) {
+            this._worker = new Worker(this);
+        }
+
+        return this._worker.send(request);
+    };
+
+    cl.poll = function(options) {
+        if(!this._worker) {
+            this._worker = new Worker(this);
+        }
+
+        return this._worker.poll(options);
+    };
+
+};

index.js

@@ -1008,6 +1008,9 @@ require("./apis/connection")(ModbusRTU);
 // add the promise API
 require("./apis/promise")(ModbusRTU);
 
+// add worker API
+require("./apis/worker")(ModbusRTU);
+
 // exports
 module.exports = ModbusRTU;
 module.exports.TestPort = require("./ports/testport");