This removes `let _ = ` from in front of `split_to` and `split_off`
and mostly follows the suggestions from the `#[must_use]` impls.
One of the uses of `split_to` is instead replaced with `take`.

- detect if run on MacOS, so we download h2spec macos build in that case
- support overwriting h2spec detection so we anyway download new file,
  useful in case you switch to new version for example
- move h2spec, archive and log all to /tmp dir as to not polute
  the repo dir

…formed (#813)

Before this change, content-length underflow is only checked when
receiving date frames. The underflow error was never triggered if
data frames are never received.

This change adds similar check for headers frames.

…ensure local stream is released properly (#816) (#818)

Similar to what have been done in fn send_reset<B>(), we should notify RecvStream that is parked after send_reset().

Co-authored-by: Jiahao Liang <gzliangjiahao@gmail.com>