Intermediate proof release.

Changelog:
 - added proof contributors
 - improved README

This signature certifies that the commits under this tag are the same as
in the internal NICTA repositories (up to sha1 collisions).

seL4 proofs, open-source release on 29 July 2014.

This signature certifies that the commits under this tag are the same as
in the internal NICTA repositories (up to sha1 collisions).