SDL_HINT_MOUSE_RELATIVE_MODE_WARP

Adding a hint from the SDL 2.0.2 RC1 build.
See: https://forums.libsdl.org/viewtopic.php?t=10053

Also added .suo files to gitignore. These contain user-specific settings that are best left out of source control. I'm mainly trying to get them to stop showing up as changed files when Visual Studio tweaks them at its own discretion.