Merge branch 'chore/rust-2021' into 'master'

Cargo.toml

build.rs

crates/common/Cargo.toml

crates/common/src/error.rs

crates/common/src/lib.rs

crates/common/src/util.rs

crates/encoding/Cargo.toml

crates/encoding/src/lib.rs

crates/hashing/Cargo.toml

crates/hashing/src/lib.rs

frontends/libretro/Cargo.toml

frontends/libretro/src/lib.rs

frontends/sdl/Cargo.toml

frontends/sdl/src/main.rs

src/cheats/genie.rs

src/cheats/shark.rs

src/cpu.rs

src/gb.rs

src/lib.rs

src/pad.rs