Made glfwGetCursorPos query system directly.

Fixes #103.
Fixes #153.
Fixes #193.
Fixes #355.
Fixes #381.

docs/input.dox

@@ -228,10 +228,6 @@ double xpos, ypos;
 glfwGetCursorPos(window, &xpos, &ypos);
 @endcode
 
-This function only returns cached cursor positions.  It does not poll the
-system for the current position.  Whenever you poll state, you risk missing the
-state change you are looking for.
-
 
 @subsection input_cursor_mode Cursor modes
 

docs/news.dox

@@ -81,6 +81,13 @@ The support for EGL is now stable, successfully running on PandaBoards, Mesa,
 ANGLE, Wayland, AMD EGL and others.
 
 
+@subsection news_31_getcursorpos Direct query for cursor position
+
+GLFW now queries the system cursor position directly when you call @ref
+glfwGetCursorPos instead of returning cached data, except for when the window is
+in captured cursor mode.
+
+
 @section news_30 New features in version 3.0
 
 @subsection news_30_cmake CMake build system