hazptr: Improve readability, specialize friends, use specialized aliases
hazptr: Improve readability, specialize friends, use specialized aliases

Summary: Use aliases. Reduce the use of the Atom template parameter.

Reviewed By: yfeldblum

Differential Revision: D29206490

fbshipit-source-id: d0637593c48ef150560b4feb47a454afe25ecba6

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly