Silk.NET.Windowing 1.2.0

Silk.NET May 2020 Update - Update to Vulkan 1.2.139 - Update to OpenCL 3.0 - Add a new context abstraction - Add extensions for using Silk.NET's Windowing API with Veldrid - Add a new way of accessing OpenGL-specific and Vulkan-specific functions - Add a helpful hint as to why your Vulkan functions are throwing EntryPointNotFoundExceptions. - Add ExtensionName constants to all extension classes (useful for Vulkan) - Add an option for waiting for events before proceeding to execute the render loop. - Add a setter to the IsClosing property so you can cancel window closure - Fix the incorrect DebugUtilsMessengerCallbackFunctionEXT signature - Fix a bug where you couldn't catch GlfwExceptions on Linux and macOS - Fix a bug where attempting to call Invoke on a window will result in a deadlock - Fix a bug where VSync was always on regardless of the requested configuration - Fix a bug where eventhough we fixed the previous VSync bug, we still weren't respecting initial vsync settings. - Fix a bug where directly accessing scroll-wheel info would return bogus data - Fix a bug where Render and Update are fired again after close - Deprecated adaptive vsync - Deprecated SilkManager - Deprecated obsolete native methods that we weren't annotating as obsolete before - Miscellaneous fixes and improvements