Update README.md

Signed-off-by: David Scott <dave.scott@citrix.com>
Add CHANGES.md

Signed-off-by: David Scott <dave.scott@citrix.com>
Add missing file: mbr_partition.mli

Signed-off-by: David Scott <dave.scott@citrix.com>
Adopt Mirage standard ISC license

Signed-off-by: David Scott <dave.scott@citrix.com>
Use a polymorphic variant result type

This allows us to easily use the same result type from other libraries,
without them being different types, needing different binds etc.

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