new editor's draft of Primer

Hi all,

Here is the latest Editors' Draft of the Primer, updated with comments
from Shane, Manu, Ralph, and Ivan. One missing piece right now is an
example with @href on a non-anchor. I left that aside because I can't
fit it in cleanly without too long an explanation: maybe it's okay to
not have this in the Primer, and instead to have this as a use case,
e.g. Joost?

Also, I still need to color the markup properly to highlight the RDFa
attributes. I'll do that in time for end of week before we ship this to
the WG.

Note that, after thinking about Shane's comment regarding duplication
between abstract and intro, I took out the abstract altogether. It seems
to me that, with such a short document, an abstract might be overkill.
Let me know if you feel it is missing, even after reading the first
couple of paragraphs.

http://www.w3.org/2006/07/SWD/RDFa/primer/20070918/

-Ben