Renamed folders for consistency, using sim/athena/shared schema (#27)

Rename the following folders:
hal/lib/Athena -> hal/lib/athena
hal/lib/Desktop -> hal/lib/sim
hal/lib/Shared -> hal/lib/shared
wpilibc/Athena -> wpilibc/athena
wpilibc/simulation -> wpilibc/sim

Windows users may need to run gradlew clean after updating.

wpilibc/sim/include/simulation/MainNode.h

@@ -0,0 +1,63 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2014-2016. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#ifndef _SIM_MAIN_NODE_H
+#define _SIM_MAIN_NODE_H
+
+#include <gazebo/gazebo_client.hh>
+#include <gazebo/transport/transport.hh>
+#include "simulation/gz_msgs/msgs.h"
+
+using namespace gazebo;
+
+class MainNode {
+ public:
+  static MainNode* GetInstance() {
+    static MainNode instance;
+    return &instance;
+  }
+
+  template <typename M>
+  static transport::PublisherPtr Advertise(const std::string& topic,
+                                           unsigned int _queueLimit = 10,
+                                           bool _latch = false) {
+    return GetInstance()->main->Advertise<M>(topic, _queueLimit, _latch);
+  }
+
+  template <typename M, typename T>
+  static transport::SubscriberPtr Subscribe(
+      const std::string& topic,
+      void (T::*fp)(const boost::shared_ptr<M const>&), T* obj,
+      bool _latching = false) {
+    return GetInstance()->main->Subscribe(topic, fp, obj, _latching);
+  }
+
+  template <typename M>
+  static transport::SubscriberPtr Subscribe(
+      const std::string& topic, void (*fp)(const boost::shared_ptr<M const>&),
+      bool _latching = false) {
+    return GetInstance()->main->Subscribe(topic, fp, _latching);
+  }
+
+  transport::NodePtr main;
+
+ private:
+  MainNode() {
+    bool success = gazebo::client::setup();
+
+    if (success) {
+      main = transport::NodePtr(new transport::Node());
+      main->Init("frc");
+      gazebo::transport::run();
+    } else {
+      std::cout << "An error has occured setting up gazebo_client!"
+                << std::endl;
+    }
+  }
+};
+
+#endif