Log Message:
SDL2: update to 2.0.18.

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2.0.18:
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General:
* The SDL wiki documentation and development headers are automatically
kept in sync
* Each function has information about in which version of SDL it
was introduced
* Added the hint SDL_HINT_APP_NAME to let SDL know the name of your
application for various places it might show up in system information
* Added SDL_RenderGeometry() and SDL_RenderGeometryRaw() to allow
rendering of arbitrary shapes using the SDL 2D render API
* Added SDL_SetTextureUserData() and SDL_GetTextureUserData() to
associate application data with an SDL texture
* Added SDL_RenderWindowToLogical() and SDL_RenderLogicalToWindow()
to convert between window coordinates and logical render coordinates
* Added SDL_RenderSetVSync() to change whether a renderer present
is synchronized with vblank at runtime
* Added SDL_PremultiplyAlpha() to premultiply alpha on a block of
SDL_PIXELFORMAT_ARGB8888 pixels
* Added a window event SDL_WINDOWEVENT_DISPLAY_CHANGED which is
sent when a window changes what display it's centered on
* Added SDL_GetWindowICCProfile() to query a window's ICC profile,
and a window event SDL_WINDOWEVENT_ICCPROF_CHANGED that is sent
when it changes
* Added the hint SDL_HINT_VIDEO_EGL_ALLOW_TRANSPARENCY to allow
EGL windows to be transparent instead of opaque
* SDL_WaitEvent() has been redesigned to use less CPU in most cases
* Added SDL_SetWindowMouseRect() and SDL_GetWindowMouseRect() to
confine the mouse cursor to an area of a window
* You can now read precise mouse wheel motion using 'preciseX' and
'preciseY' event fields
* Added SDL_GameControllerHasRumble() and
SDL_GameControllerHasRumbleTriggers() to query whether a game
controller supports rumble
* Added SDL_JoystickHasRumble() and SDL_JoystickHasRumbleTriggers()
to query whether a joystick supports rumble
* SDL's hidapi implementation is now available as a public API in
SDL_hidapi.h

Linux:
* Added the hint SDL_HINT_SCREENSAVER_INHIBIT_ACTIVITY_NAME to set
the activity that's displayed by the system when the screensaver
is disabled
* Added the hint SDL_HINT_LINUX_JOYSTICK_CLASSIC to control whether
/dev/input/js* or /dev/input/event* are used as joystick devices
* Added the hint SDL_HINT_JOYSTICK_DEVICE to allow the user to
specify devices that will be opened in addition to the normal
joystick detection
* Added SDL_LinuxSetThreadPriorityAndPolicy() for more control over
a thread priority on Linux