Viewers can be defined by content type as well, for aggregate objects such as books.
Merge branch '7.x' into 7.x-allow-viewers-based-on-content-type
Merge branch '7.x' into 7.x-allow-viewers-based-on-content-type
Updated function header.
Parameters documented for viewer functions.
Merge pull request #230 from nigelgbanks/7.x-allow-viewers-based-on-content-type

7.x allow viewers based on content type
Updated README to include the XACML policies

Included the necessary XACML policies in the repository. Added
information about them to the README.
Merge pull request #232 from jonathangreen/7.x

Updated README to include the XACML policies