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/simTime.h

@@ -0,0 +1,26 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#ifdef _WIN32
+// Ensure that Winsock2.h is included before Windows.h, which can get
+// pulled in by anybody (e.g., Boost).
+#include <Winsock2.h>
+#endif
+
+#include "simulation/SimFloatInput.h"
+
+#include <condition_variable>
+#include <mutex>
+
+namespace wpilib {
+namespace internal {
+extern double simTime;
+extern void time_callback(const msgs::ConstFloat64Ptr& msg);
+}
+}