added conversion from PixelFormatEnum to PixelFormat
added conversion from PixelFormatEnum to PixelFormat

Rust-SDL2/rust-sdl2,AngryLawyer/rust-sdl2,Rust-SDL2/rust-sdl2,Cobrand/rust-sdl2,Rust-SDL2/rust-sdl2,Cobrand/rust-sdl2,Cobrand/rust-sdl2