OpenTK 3.1.0

General: * Fixed problem where OpenGL 3.2 contexts where created using the wrong flags, causing renderdoc error (#790). * Fixed problem where Vector3.Transform(Quaternion) returned incorrect results ( #776 ). * SDL backend no longer handles exceptions thrown in input events ( #735 #737 ) * Updated gamepadd mappings for SDL (#927). * Alt + numpad now results in correct data being passed to OnKeyPress (f17fa4b). Windows: * Keypress events are using CharSet.Unicode to allow for UTF characters. * If GetMouseMovePointsEx returns "access denied" we fall back to the old mouse move handling ( #883 ). * Detect joysticks which declare no valid controls & ignore (Cherry-picked from #819 ). * Fix where an invalid joystick axis overwrites the first joystick axis. (Cherry-picked from #819 ). * Makes the ArbCreateContext return valid settings ( #754 ). MacOS: * Unprocessed events no longer put the application into a partially-activated state ( #732 ). * Multiple fixes under PR #914: * NativeWindow.CursorVisible no longer resets the mouse position ( #668 ). * Custom cursors should work now ( e598ab2 ). * Command key is now a valid modifier ( 286119e ). * Fix where KeyDown events would trigger KeyPress when they shouldn't, e.g. when pasting ( ea3dd48 ). * KeyPress now receives the correct keycodes even if modifiers where held when typing ( 91b03dd ). Internal: * Generator.Build now uses invariant culture for parsing avoiding an exception when the local system uses comma as decimal separator ( #750 ). * Removed weird assembly version check fixing #710. * Fixed Xamarin project so that it compiles ( See #725 and b16e7fa ). * Matrix4 uses unsafe to invert for performace ( #719 ). * Removed link to gitter chat, discord is where it's at ( #770 ).