Schedule: datatypes document plan

At last Friday's telecon we discussed how to proceed with the datatypes 
document.

I believe the following suggestion was made and found support:

   o that we publish a datatyping WD

   o the we reaffirm our decision that the datatyping work is rec track

   o that we keep open the option of merging the datatyping WD into other 
documents in the future (likely schema and model theory)

To keep things moving along, I propose that we adopt this plan.

Brian