delete unused variable

Test Plan: none

Reviewed By: tjackson@fb.com

FB internal diff: D818326
Gen apply comment

Summary: Comment

Test Plan: Builds

Reviewed By: tjackson@fb.com

FB internal diff: D814986
Allow escapeString in folly/json.cpp to be called by other methods.

Summary: See title.

Test Plan:
From fbocde, type:
fbconfig folly/test; fbmake opt -j 32; fbmake runtests_opt -j 32

Reviewed By: delong.j@fb.com

FB internal diff: D818077
Add folly::lazy

Summary:
A thin wrapper around Optional for terse creation of
lazily-initialized values.

Test Plan: New tests, and a use case in hphp.

Reviewed By: tjackson@fb.com

FB internal diff: D817906
Some documentation updates in lazy

Summary: Per discussion after commit on the previous diff.

Test Plan: Compiled.

Reviewed By: tjackson@fb.com

FB internal diff: D821985