Use a temporary private fork of tokio-rustls that uses Rustls 0.12
until tokio-rustls 0.4 is released.
This upgrades, among other things, *ring* to 0.12, which will ensure
that it still builds in the Rust 1.20 release coming this week even if
backward-compatibility-breaking changes to rustc aren't fixed before
the release.
Because, you might think that each linked list has exclusive access to
the next pointer, but then there is an edge case that proves otherwise.
Also, debugging this kind of thing is annoying.
Restructure send flow control such that sending data is always accepted by `Stream`. Data frames will be buffered until there is available window to send them. Producers can monitor the available window capacity to decide if data should be produced.
With this change, h2 can build and run without any manual configuration steps for -msvc targets. Previously manual installation of OpenSSL libraries was required.
tokio-io 0.1.3 has been published so the "replace" for tokio-io 0.1.2 is no longer useful and it breaks the build with some (but apparently not all) versions of Cargo.
Update the dependency to tokio-io 0.1.3 since that is the version that's what's been verified to work.
Client::poll_ready ensures that the connection is ale to to initiate a new request stream to the remote server. When the server is at capacity, a task is stored to be notified when capacity is available.
