[pph] wiki page set up

[Diego Novillo]

I finally found some time to write some documentation for the branch.
I've created http://gcc.gnu.org/wiki/pph with some initial
documentation on the pre-tokenization and pre-parsing work we are
doing on the branch.

The big missing piece is a more detailed design document that Lawrence
will be posting in the next few days.

Lawrence, Ben, Jason, could you take a look and make sure things make sense?

I've also updated svn.html with the location of the branch.


Thanks.  Diego.