Added Atom Plugin

Summary: Closes https://github.com/facebook/hhvm/pull/4340

Reviewed By: @jwatzman

Differential Revision: D1704784

Signature: t1:1704784:1417477025:60ed0dda7a390b78faceb5df9f6790ca1619d055
EZC: fix 'Z' type in zend_parse_parameters()

Summary: For both 'Z' and vararg '*' types in zend_parse_parameters(), a zval**
needs to be returned to the caller. I previously thought that temporary
storage would be needed for this, but in fact you can just point to the
TypedValue pref member.
Closes https://github.com/facebook/hhvm/pull/4330

Reviewed By: @sgolemon

Differential Revision: D1701584

Signature: t1:1701584:1417478162:f5f16e0305079f1f8552329a0b0ad5461497c516