increase Video plugin API to v2.2.0, add new ResizeVideoOutput function
video extension API version is increased to v3.0.  This adds a new Flags parameter to the VidExtSetVideoMode() function, and adds a new function VidExt_ResizeWindow.  This is to support resizable output windows
1. Update FRONTEND_API_VERSION to v2.1.1: Core command M64CMD_CORE_STATE_SET will now accept M64CORE_VIDEO_SIZE parameter (will call the video plugin function ResizeVideoOutput())
2. Capture SDL_VIDEORESIZE events and call video plugin ResizeVideoOutput() function.
3. In VidExt_ResizeWindow(), destroy and re-create OSD when re-setting the screen size
4. Fix bug when checking video api version for <2.2.0 fallback
add some more developer documentation regarding the window resizing functionality