The `Request` and `Response` module types now explictly signal `Eof`
and `Invalid` (for errors), to help the backend distinguish them.

Also fixes pipeline handling for multiple requests in Async.

Closes #94
enable nettests by default
Merge pull request #97 from avsm/fix-pipelining

The `Request` and `Response` module types now explictly signal `Eof`