Range library for C++14/17/20. This code was the basis of a formal proposal
to add range support to the C++ standard library. That proposal evolved
through a Technical Specification, and finally into P0896R4 "The One Ranges
Proposal" which was merged into the C++20 working drafts in November 2018.

Ranges are an extension of the Standard Template Library that makes its
iterators and algorithms more powerful by making them composable. Unlike
other range-like solutions which seek to do away with iterators, in range-v3
ranges are an abstration layer on top of iterators.