P1252 Ranges Design Cleanup

[jensmaurer]

P1252R1 Ranges Design Cleanup (Casey Carter)

https://issues.isocpp.org/show_bug.cgi?id=546

[mclow]

LWG reviewed and approved on Friday in Kona.

[jensmaurer]

Approved by plenary in Kona; see cplusplus/draft#2707.

[wg21bot]

P1252R2 Ranges Design Cleanup (Casey Carter)

[wg21bot]

Adopted 2019-03.