NM-DM-3: CDATA support in Data Model

Data model should support cdata sections. Preserving of cdata in input documents can be
controlled by flag in static context (and declaration in xslt/query prolog).
Without this it would be impossible to preserve structure of document durning transformations.
(it's especially big problem for nearly-identity transformations than changes only small parts of original document).
There are also other uses, such as xpath based search & replace option in XML editors
(ability to find and modify cdata sections) and finer control in XSLT over which content is serialized as cdata.

This will need cdata constructors in XSLT and XQuery, and cdata() SequenceType.
Maybe this feature can wait to V3.0, but will be needed at some point.

Best Regards,
Noe Michejda
7th Portal S.C.