Move TcpTuple into tcp.go
Improve logging of TcpTuple structs

Previously:

{%!s(uint32=167772674) %!s(uint32=167772687) %!s(uint16=49779)
%!s(uint16=80) %!s(uint32=1)}

Now:

src[10.0.2.2:49813] dst[10.0.2.15:80] stream_id[1]
Merge pull request #16 from lmars/improve-logging

Improve logging