Updated state of foreign memory/function access docs

[Maurizio Cimadamore]

Hi,
following the recent API twists, I've updated the documents capturing 
the state of the foreign memory access API and the foreign linker API; 
they can be found here:

http://cr.openjdk.java.net/~mcimadamore/panama/foreign-memaccess.html
http://cr.openjdk.java.net/~mcimadamore/panama/ffi.html

There's an header in both documents describing what changed compared to 
previous version.

Cheers
Maurizio