Merge branch 'v0.4.x' into uplift-0.4-commits

.travis.yml

CHANGELOG.md

Cargo.toml

README.md

ci/tsan

src/buf/buf.rs

src/buf/buf_mut.rs

src/buf/mod.rs

src/buf/reader.rs

src/buf/vec_deque.rs

src/bytes.rs

src/either.rs

src/lib.rs

tests/test_bytes.rs

tests/test_reader.rs