Adds new Threads API for priority setting while using std::thread (#379)

Also adds Java API for doing the same to Java threads (standard Java Thread.setPriority only works
when Java is run as root, even if the process has the right privileges).

wpilibc/athena/include/Threads.h

@@ -0,0 +1,18 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 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
+
+#include <thread>
+
+namespace frc {
+
+int GetThreadPriority(std::thread& thread, bool* isRealTime);
+int GetCurrentThreadPriority(bool* isRealTime);
+bool SetThreadPriority(std::thread& thread, bool realTime, int priority);
+bool SetCurrentThreadPriority(bool realTime, int priority);
+}  // namespace frc