Add _oasis version constraints (cohttp >= 0.10.0 and cstruct >= 0.6.0)

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

Signed-off-by: David Scott <dave.scott@citrix.com>
Release 0.6.1

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