added cfg attr to denote required tcp feature in docs for Client::new method

Closes: #2759

This adds `local_addr` information from `TcpStream` to the `HttpInfo` struct

Closes #2767

Remove unconditional building of FFI libraries: now
that nightly supports --crate-type, it can be opted into.
This fixes cargo's pipelining both for dependencies and
for dependent crates, resulting in faster from-scratch builds.

Now that FFI is opt-in using cargo's --crate-type, nightly needs to be used
on CI: this flag is still unstable and requires a nightly to enable -Z unstable options.

Update the command to use `--crate-type`.