Update specification for "Remote Atomics"

[Dan Bonachea]

This issue is a placeholder to track specification progress on the March 18 STPM17-7 milestone deliverable:

Implement new “Remote Atomics” APIs utilizing corresponding GASNet-EX feature in STPM17-6; write or update the corresponding specification; and provide corresponding tests and/or examples.

The corresponding GASNet-EX feature is specified here.

Much of the current discussion on this topic resides in issue #20

[Dan Bonachea]

Fixed by merge of pull request #8 in 0b61e76