[Beignet] Code freeze for version 0.9.0 release

[Zhigang Gong]

Hi folks,

Beignet is approaching next version release. And we will freeze the master branch
from the comming Monday (6/13). After that, we will only accept bug fixes and
document update patches before the release.

If you have some important patches in hand which you want it to be merged in
next release, please send it out ASAP. Thanks.