Cleanup some Surface function signatures
Cleanup some Surface function signatures

* Remove lock and unlock methods from Surface
The lock/unlock methods aren't that useful by themselves, so they've been
removed in favor of with_lock.

* Make enable_RLE and disable_RLE accept &mut self
These methods could interfere with the underlying Surface buffer,
so they must mutate Surface.

* Remove Surface::convert_format; it is redundant to Surface::convert

* Wherever SdlResult<> is unnecessary, remove it

Cobrand/rust-sdl2,beni55/rust-sdl2,Rust-SDL2/rust-sdl2,crumblingstatue/rust-sdl2,vadixidav/rust-sdl2,Cobrand/rust-sdl2,bvssvni/rust-sdl2,caldwell/rust-sdl2,Cobrand/rust-sdl2,oldmanmike/rust-sdl2,inrustwetrust/rust-sdl2,AngryLawyer/rust-sdl2,tempbottle/rust-sdl2,bfops/rust-sdl2,wilsoniya/rust-sdl2,Rust-SDL2/rust-sdl2,Rust-SDL2/rust-sdl2