To further distance the code from having to do too much manually, the graphics context is now available as a managed class. All places that previously used obs_enter_graphics and obs_leave_graphics are now using the new gs::context class instead.
Box Blur is a prime candidate for Linear optimizations, and as such reducing the total necessary samples by about half. However due to the reduction in samples, only Area and Directional Blur are supported.
Related: #45, #6
