fixed race condition in the signalling between the rx and tx threads
Changed default ack scheme from delayed to immediate

The immediate ack scheme is the better choice for more use cases.
move listen_tcpv4 callback to an async thread
(allowing the listener to accept the next client)
unix: fix `Eof on empty TCP.write
Improve opam and travis files
Merge pull request #77 from samoht/master

Improve opam and travis files
Sync for 2.0.0 release
Merge pull request #75 from lnmx/fix-accept

move listen_tcpv4 callback to an async thread
Merge pull request #76 from pqwy/write-errors

unix: fix `Eof on empty TCP.write
Merge branch 'master' of git://github.com/mirage/mirage-tcpip
travis: add a mirage-dev remote
Merge pull request #78 from avsm/master

Release 2.0.0
Merge branch 'master' of git://github.com/balrajsingh/mirage-tcpip into balrajsingh-master

Conflicts:
	tcp/segment.ml
bump to version 2.0.1
Merge pull request #79 from avsm/master

Release 2.0.1
Add cstruct for ipv6 packet header
Initial commit of IPV6 module
Add cstruct for icmpv6
Add ipv6 checksum computation
Drop icmp6 packet if checksums don't match