Standard references should be updated to N4849

[BillyONeal]

In the January of 2020 mailing, a new version of the C++ standard, N4849 is available (https://wg21.link/std as of this writing). We should find all the N\d\d\d\d standard references and update their N number and paragraph reference to the latest working paper.

[BillyONeal]

(To do this, grep the source tree for N\d\d\d\d, find the [stable.name] in the new standard, find the appropriate corresponding paragraph number, and update any quoted standards text as appropriate)

[StephanTLavavej]

This is a duplicate of #182.

[BillyONeal]

It seems like the way #182 is formulated it can never be completed though. It seems like we should have a specifically actionable "update to N1234" issue created whenever a new WP comes out.

[StephanTLavavej]

In the discussion for #182, we had tentatively decided on an initial cleanup to the current WP, followed by successive issues for each published standard - because yes, it is an evergreen task, but updating to literally every new WP is not necessary.