Add the ability to include meta-data to appear as attributes in Acrobat

[CapnK]

See: http://sourceforge.net/p/u3d/discussion/557102/thread/52487a66/
and the META_DATA block documentation for IDTF

Add the ability to write meta-data tags which contain an RHAdobeMeta tag, which contains a set of pseudo XML attribute tags.

No other uses of the META_DATA tag are known, but it may be best implemented as a generic META_DATA list, with a special RHAdobeMeta entry.

Note, the meta_data block can be applied to a number of different IDTF nodes/resources, but it appears that the meta-data on the 'MODEL' node is transferred into Adobe Reader (not the meta-data on the MESH resource)

Also the META_DATA block must be the last block contained within it's parent block

[CapnK]

RHAdobe metadata and generic string meta data implemented for IDTF 'Node' types (Model, View, Light, Group) Only tested on the 'Model' nodes
Binary meta data not implemented