Add CSSOM.
Merge pull request #125 from tobie/cssom

Add CSSOM.
Merge pull request #126 from fhirsch/develop

update publication date for xmlsec publications
integrated Steve's patch by hand
start of implementation of serializer keyword
(cherry picked from commit 74603ea0c780105a1e26d9281d643f8e0aa50e1b)
template for serializer
(cherry picked from commit 66b0ec120b6fcd0915c4e31bd64892e4fc7af548)
Support for serializer syntax in WebIDL
(cherry picked from commit f2510a9fc921cd00888523935f0a1b3c3ee79d89)
v3.1.19
Merge branch 'release/v3.1.39' into develop
make README clearer on which branch to PR against