Extensibility for folly::to<> through ADL
Extensibility for folly::to<> through ADL

Summary: Primarily to support slightly more flexible implementations of `split()`;

Reviewed By: ot

Differential Revision: D3116763

fb-gh-sync-id: 69023c0f26058516f25b9c1f9824055efc7021f9
fbshipit-source-id: 69023c0f26058516f25b9c1f9824055efc7021f9

yqzhang/mcrouter,yqzhang/mcrouter,facebook/mcrouter,yqzhang/mcrouter,facebook/mcrouter,yqzhang/mcrouter,facebook/mcrouter,facebook/mcrouter