[NRY] Make net.TCPSocket implement Stream.Duplex

...at least enough to run this test:
https://forums.tessel.io/t/socket-pipe-not-working-as-expected/204

Don't merge yet. I'm going to see how many of the TODOs I can fix with the current CC3K driver (should fit the async one nicely).
@tcr, is it expected that the HTTP parser is unable to handle a Buffer? What about requesting binary files over HTTP?