GitHub anchor links and Website anchor links are different

[aarongable]

When using github to render the markdown, section anchor links look like #32-initial-identity-validation.

However, the section anchor links on our website have dots between their numbers, like 3.2-initial-identity-validation.

This means that all of the anchor links in use currently work correctly on github but not on the website. We should see if we can change the way the website generates heading anchors to match the way github does it, so the same links work in both locations.

[aarongable]

(If we succeed, we should also update the CP/CPS to consistently use section cross-links throughout, instead of using them in some places like Section 1.3.2, but not using them in others like Section 2.1.)