Merge branch 'signals' into 'master'

Cargo.lock

Cargo.toml

src/header/signal/mod.rs

src/header/sys_time/mod.rs

src/header/unistd/mod.rs

src/macros.rs

src/platform/auxv_defs.rs

src/platform/linux/signal.rs

src/platform/mod.rs

src/platform/pal/signal.rs

src/platform/redox/clone.rs

src/platform/redox/exec.rs

src/platform/redox/mod.rs

src/platform/redox/path.rs

src/platform/redox/ptrace.rs

src/platform/redox/redox-exec/Cargo.toml

src/platform/redox/redox-exec/src/lib.rs

src/platform/redox/signal.rs

src/pthread/mod.rs

src/start.rs