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).

hal/include/HAL/Threads.h

@@ -0,0 +1,26 @@
+/*----------------------------------------------------------------------------*/
+/* 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 "HAL/Types.h"
+
+#ifdef _WIN32
+#include <windows.h>
+#define NativeThreadHandle const HANDLE*
+#else
+#include <pthread.h>
+#define NativeThreadHandle const pthread_t*
+#endif
+
+int32_t HAL_GetThreadPriority(NativeThreadHandle handle, HAL_Bool* isRealTime,
+                              int32_t* status);
+int32_t HAL_GetCurrentThreadPriority(HAL_Bool* isRealTime, int32_t* status);
+HAL_Bool HAL_SetThreadPriority(NativeThreadHandle handle, HAL_Bool realTime,
+                               int32_t priority, int32_t* status);
+HAL_Bool HAL_SetCurrentThreadPriority(HAL_Bool realTime, int32_t priority,
+                                      int32_t* status);