Implement -location flag

Includes locationId in the keyboards identifiers (defaults to false)

Note that the locationId changes when you plug a keyboard in a different port.
Therefore using the locationId in the keyboards identifiers means the
configured language will be associated to a keyboard on a specific port.

fixes #6

autokbisw/IOKeyEventMonitor.swift

@@ -80,13 +80,15 @@ final internal class IOKeyEventMonitor {
       let locationId = String(describing: IOHIDDeviceGetProperty(senderDevice, kIOHIDLocationIDKey as CFString));
       let uniqueId = String(describing: IOHIDDeviceGetProperty(senderDevice, kIOHIDUniqueIDKey as CFString));
 
-      let keyboard = "\(product) - [\(vendorId)-\(productId)-\(manufacturer)-\(serialNumber)]";
+      let keyboard =
+      selfPtr.userOptions.useLocation ?
+      "\(product)-[\(vendorId)-\(productId)-\(manufacturer)-\(serialNumber)-\(locationId)]" :
+      "\(product)-[\(vendorId)-\(productId)-\(manufacturer)-\(serialNumber)]";
 
       if(selfPtr.userOptions.verbosity >= UserOptions.TRACE){
          print("received event from keyboard \(keyboard) - \(locationId) -  \(uniqueId)");
       }
-      selfPtr.onKeyboardEvent(keyboard: keyboard);
-
+      selfPtr.onKeyboardEvent(keyboard: keyboard);    
     }
 
     IOHIDManagerRegisterInputValueCallback( hidManager, myHIDKeyboardCallback, context);