LGPL code has been removed, license is now ISC

This patch also adds a LICENSE file plus a list of copyright holders
taken from all the source files.

Note that this library still depends on hashcons, which is LGPL2.1 + OCaml
linking exception.

Fixes #7

Signed-off-by: David Scott <dave.scott@docker.com>

LICENSE

@@ -0,0 +1,22 @@
+Copyright (c) 2015 Luke Dunstan <LukeDunstan81@gmail.com>
+Copyright (c) 2015 Heidi Howard <hh360@cam.ac.uk>
+Copyright (c) 2013-2015 David Sheets <sheets@alum.mit.edu>
+Copyright (c) 2014 marklrh <marklrh@gmail.com>
+Copyright (c) 2005-2014 Anil Madhavapeddy <anil@recoil.org>
+Copyright (c) 2011-2012 Richard Mortier <mort@cantab.net>
+Copyright (c) 2011-2014 Anil Madhavapeddy <anil@recoil.org>
+Copyright (c) 2005-2006 Tim Deegan <tjd@phlegethon.org>
+Copyright (c) 2005 Fraser Research Inc. <djs@fraserresearch.org>
+
+Permission to use, copy, modify, and/or distribute this software for any
+purpose with or without fee is hereby granted, provided that the above
+copyright notice and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+

opam

@@ -13,7 +13,7 @@ authors: [
   "Luke Dunstan"
   "David Scott"
 ]
-license: "LGPL-2.0 &\n   LGPL-2.1 with OCaml linking exception &\n   ISC"
+license: "ISC"
 tags: [
   "org:mirage"
   "org:xapi-project"