NuGet
#ADD: Added NuGet binaries, specs and package building batch file.
Added SDL2 haptic support for gamepads and joysticks.
Merge branch 'sdl2-haptics' into master-onikira
Updated gamepad mappings for default controllers on windows.
GamePadConfiguration will now parse hat values.
Updated Sdl2Factory so that the Sdl2JoystickDriver path is used for gamepads
when using SDL.
Merge branch 'master' of https://github.com/BraveSirAndrew/opentk into master-onikira

Conflicts:
	Source/OpenTK/Input/GamePadConfigurationDatabase.cs
	Source/OpenTK/Input/JoystickCapabilities.cs
	Source/OpenTK/Platform/Linux/LinuxJoystick.cs
	Source/OpenTK/Platform/MacOS/HIDInput.cs
	Source/OpenTK/Platform/SDL2/Sdl2.cs
	Source/OpenTK/Platform/SDL2/Sdl2JoystickDriver.cs
	Source/OpenTK/Platform/Windows/WinMMJoystick.cs
[Input] Implemented JoystickHat GamePad mapping
[Input][SDL] Fix JoystickHat bugs

On SDL, DPad inputs were not correctly translated from joystick
hat inputs.
Updated MappedGamePadDriver so that it will correctly recognize
combined joystick hat directions e.g. DPadLeft should be true when
DownLeft, Left, or UpLeft are returned from the joystick hat.