Merge latest upstream of 'bytes' library into 'bytes-sgx'

We're currently creating a SGX-supported fork of [tungstenite](https://github.com/integritee-network/tungstenite-rs-sgx). The [bytes](https://github.com/tokio-rs/bytes) library is a low-level dependency for multiple other dependencies of tungstenite.

Unfortunately the [SGX fork](https://github.com/mesalock-linux/bytes-sgx) is not up-to-date enough to support new versions of tungstenite (which we need, in order to have the rustls feature). There is a pending upstream merge [PR](https://github.com/mesalock-linux/bytes-sgx/pull/3) with a few minor merge conflicts. Could you incorporate those changes and bump the version?
(I've done so myself as a [temporary solution](https://github.com/integritee-network/bytes-sgx), but I don't think it's wise to maintain yet another fork)

Review the linked bytes-sgx repository and pending upstream PR #3 first, then compare the fork with the current tokio-rs/bytes changes and identify the merge conflicts. Done means incorporating the upstream changes and bumping the bytes-sgx version so newer tungstenite versions with rustls support can use it.

Written by the indexing model from the issue text.