Extend kj::Network interface for easy SSRF protection

Clarify the RPC spec in some places

Add gzip (zlib) bindings.

E.g.:

    "foo"_kj

This literal will have type StringPtr. Although any string literal can implicitly cast to StringPtr, using the _kj suffix has the advantage that it can be constexpr.

ubsan: cast to unsigned integer before performing left shift

Implement TLS option to verify client certificates.

Use case for me is Cloudflare's "Authenticated Origin Pulls", in which Cloudflare authenticates itself to the origin server using client certificates. Thus the origin server can ensure that it only accepts traffic through Cloudflare, without resorting to IP whitelists.

This really is more of a data structure than a resource type, and it's useful to be able to share it between threads and whatnot.

buffers passed to PackedOutputStream::write() must be word-aligned

avoid passing invalid reference to Array<T> constructor

ubsan complains about the invalid reference even if it is unused.

RPC: Support abstract unix socket addresses on Linux

Add WebSocket support to HTTP library