Added a hint to control the Windows timer resolution: SDL_HINT_TIMER_RESOLUTION

Added an API to watch hint changes: SDL_AddHintCallback(), SDL_DelHintCallback()
You can now dynamically set the joystick background event hint.

include/SDL_hints.h

@@ -218,13 +218,13 @@ extern "C" {
 /**
  *  \brief  A variable that lets you enable joystick (and gamecontroller) events even when your app is in the background.
  *
- * The default value is "0".
- *
  *  The variable can be set to the following values:
  *    "0"       - Disable joystick & gamecontroller input events when the
  *                application is in the background.
  *    "1"       - Enable joystick & gamecontroller input events when the
  *                application is in the backgroumd.
+ *
+ *  The default value is "0".  This hint may be set at any time.
  */
 #define SDL_HINT_JOYSTICK_ALLOW_BACKGROUND_EVENTS "SDL_JOYSTICK_ALLOW_BACKGROUND_EVENTS"
 
@@ -240,6 +240,23 @@ extern "C" {
 #define SDL_HINT_ALLOW_TOPMOST "SDL_ALLOW_TOPMOST"
 
 
+/**
+ *  \brief A variable that controls the timer resolution, in milliseconds.
+ *
+ *  The higher resolution the timer, the more frequently the CPU services
+ *  timer interrupts, and the more precise delays are, but this takes up
+ *  power and CPU time.  This hint is only used on Windows 7 and earlier.
+ *
+ *  See this blog post for more information:
+ *  http://randomascii.wordpress.com/2013/07/08/windows-timer-resolution-megawatts-wasted/
+ *
+ *  If this variable is set to "0", the system timer resolution is not set.
+ *
+ *  The default value is "1". This hint may be set at any time.
+ */
+#define SDL_HINT_TIMER_RESOLUTION "SDL_TIMER_RESOLUTION"
+
+
 
 /**
  *  \brief  An enumeration of hint priorities
@@ -273,7 +290,6 @@ extern DECLSPEC SDL_bool SDLCALL SDL_SetHintWithPriority(const char *name,
 extern DECLSPEC SDL_bool SDLCALL SDL_SetHint(const char *name,
                                              const char *value);
 
-
 /**
  *  \brief Get a hint
  *
@@ -281,6 +297,29 @@ extern DECLSPEC SDL_bool SDLCALL SDL_SetHint(const char *name,
  */
 extern DECLSPEC const char * SDLCALL SDL_GetHint(const char *name);
 
+/**
+ *  \brief Add a function to watch a particular hint
+ *
+ *  \param name The hint to watch
+ *  \param callback The function to call when the hint value changes
+ *  \param userdata A pointer to pass to the callback function
+ */
+typedef void (*SDL_HintCallback)(void *userdata, const char *name, const char *oldValue, const char *newValue);
+extern DECLSPEC void SDLCALL SDL_AddHintCallback(const char *name,
+                                                 SDL_HintCallback callback,
+                                                 void *userdata);
+
+/**
+ *  \brief Remove a function watching a particular hint
+ *
+ *  \param name The hint being watched
+ *  \param callback The function being called when the hint value changes
+ *  \param userdata A pointer being passed to the callback function
+ */
+extern DECLSPEC void SDLCALL SDL_DelHintCallback(const char *name,
+                                                 SDL_HintCallback callback,
+                                                 void *userdata);
+
 /**
  *  \brief  Clear all hints
  *