The weston-layout library supports

API set of controlling properties of surface and layer which groups
surfaces. An unique ID whose type is integer is required to create
surface and layer. With the unique ID, surface and layer are identified
to control them. The API set consists of APIs to control properties of
surface and layers about followings,

- visibility.
- opacity.
- clipping (x,y,width,height).
- position and size of it to be displayed.
- orientation per 90 degree.
- add or remove surfaces to a layer.
- order of surfaces/layers in layer/screen to be displayed.
- commit to apply property changes.
- notifications of property change.

Signed-off-by: Nobuhiko Tanibata <NOBUHIKO_TANIBATA@xddp.denso.co.jp>