Use ocaml-tuntap allowing us to delete now redundant code. No functionality change.
Merge pull request #26 from vbmithr/master

Added documentation
Merge pull request #28 from vbmithr/tuntap-integration

Tuntap integration, to pull after my other PRs
Improved function Netif.create for the Xen backend. Now the cleaning code should be called on failure