Document image data being non-premultiplied

Fixes #426.

docs/input.dox

@@ -296,8 +296,9 @@ GLFWcursor* cursor = glfwCreateCursor(&image, 0, 0);
 If cursor creation fails, `NULL` will be returned, so it is necessary to check
 the return value.
 
-The image data is 32-bit RGBA, i.e. eight bits per channel.  The pixels are
-arranged canonically as sequential rows, starting from the top-left corner.
+The image data is 32-bit, little-endian, non-premultiplied RGBA, i.e. eight bits
+per channel.  The pixels are arranged canonically as sequential rows, starting
+from the top-left corner.
 
 
 @subsubsection cursor_standard Standard cursor creation

include/GLFW/glfw3.h

@@ -2601,9 +2601,9 @@ GLFWAPI void glfwSetCursorPos(GLFWwindow* window, double xpos, double ypos);
  *  glfwSetCursor.  The cursor can be destroyed with @ref glfwDestroyCursor.
  *  Any remaining cursors are destroyed by @ref glfwTerminate.
  *
- *  The pixels are 32-bit little-endian RGBA, i.e. eight bits per channel.  They
- *  are arranged canonically as packed sequential rows, starting from the
- *  top-left corner.
+ *  The pixels are 32-bit, little-endian, non-premultiplied RGBA, i.e. eight
+ *  bits per channel.  They are arranged canonically as packed sequential rows,
+ *  starting from the top-left corner.
  *
  *  The cursor hotspot is specified in pixels, relative to the upper-left corner
  *  of the cursor image.  Like all other coordinate systems in GLFW, the X-axis