[css-position] Remove the clip property, as the masking spec defines it more sensibly.
[css-shapes] Added a margin-box example
[css-shapes] Updated computed value and serialization of basic shapes
[css-shapes] add disposition source
[mediaqueries] Define <media-feature-list>

--HG--
extra : rebase_source : 45105001443e9e22f2009f9082bbf76d2e41b424
[css-shapes] add property section summaries