This package has moved into go-libp2p as a sub-package, github.com/libp2p/go-libp2p/p2p/muxer/mplex.
This is an implementation of the go-stream-muxer interface for multiplex. For more information, see that repo.
go get -d github.com/libp2p/go-libp2p-mplex
cd $GOPATH/src/github.com/libp2p/go-libp2p-mplex
make deps