Usage of deprecated std::num::FromPrimitive

[HolgerPeters]

Trying to get rust-sdl working, I found that events.rs uses std::num::FromPrimitive which has been removed from rust by now (see rust-lang/rust#16920 for more information). Thus, rust-sdl will not compile with newest rust.

~/.cargo/git/checkouts/rust-sdl-917d0a231cab7c3c/master/src/sdl/event.rs:4:5: 4:28 error: unresolved import std::num::FromPrimitive. There is no FromPrimitive in std::num

[lgrz]

Thanks!