crange, and range const overloads

crange, and range const overloads

Summary:
[Folly] `crange`, and `range` `const` overloads.

Instead of using universal reference for `range` overloads, bifurcate explicitly between `&` and `const&` overloads. The `&` overloads return `Range<T*>` while the `const&` overloads return `Range<T const*>`.

Add `crange` overloads, which may accept non-`const` arguments but will return `Range<T const*>` results anyway.

Reviewed By: ot

Differential Revision: D6242038

fbshipit-source-id: bc373c3288ea88792f04b49a372262d12204b586