bump working version to 0.9.9
* Move `OS.Clock` out to a toplevel `Clock` module (the `mirage-clock` package).
* Move `OS.Io_page` out to a toplevel `Io_page` module (the `io-page` package).
[travis] update dependent packages
Add (untested) mir-xen-build script to link the Xen kernel from an output-obj
[unix] Remove `tuntap` stubs from Unix module; they are in `ocaml-tuntap` now.
remove tap stubs
[unix] remove blkif, console and devices modules in preparation
Remove Xen packages that are now separate
Merge git://github.com/avsm/mirage-platform

Conflicts:
	CHANGES
	unix/_vars
	xen/_vars
	xen/lib/oS.mlpack
xen: update META deps
unix: remove tuntap dep, as that's needed by netif only
Update library dependencies to reduce them based on new functionality.
Install library as `mirage-xen` or `mirage-unix` that can coexist.
update travis
travis: fix opam deps
travis: boot the latest repository rather than the http remote
fix typo in unix META file (io-page-xen -> io-page-unix)
Merge pull request #76 from avsm/master

Disaggregate Mirage platform for 1.0.0