Add convenience method for folly::join
Summary: While folly has join methods that return a string (and thus don't need a string referenced passed), it does not support this idiom with iterators. This diff adds support for calls like folly::join("/", itr.begin(), itr.end() - 1).
Test Plan: Unit test
Reviewed By: njormrod@fb.com
Subscribers: philipp, trunkagent, njormrod, folly-diffs@, yfeldblum
FB internal diff:
D1702892
Tasks:
5691439
Signature: t1:
1702892:
1418344206:
9c1736f5d8e41be1df71a415e3803fe846b387b7