fragments comments

I've added some comments to the frags doc.

Note that these do not constitute the promised HP review of OWL-R which 
I expect in the next few days, and maybe very short - along the lines of:

"We expect to implement this."

I haven't marked those issues that are critical - if I have time on 
Monday I will mark those review comments that IMO, must be addressed 
before FPWD, and those that I would at least like to be explicit as open 
issues or to-do so that the reader can see that these aspects of the 
WIP. The vast majority of my comments can wait until after FPWD.

I think critical comments are:
   title, copyright and abstract

with intro as near-critical.

Jeremy