[IPP] [PWG5100.5] Issue #81: Add "ipp-features-supported" value 'document-object' currently registered in 5100.13

[msweet at apple.com]

[Issue Unconfirmed]

5100.13 defines ipp-features-supported, so that is the correct place to
leave the initial definition of "document-object" (since 5100.5 came before
5100.13...)

Link: http://www.pwg.org/issues/81