Encapsulate page layout for formats - Part 1

[Bellangelo]

Partially addresses: #1823

A rendered result can be seen here: https://bellangelo.github.io/OpenAPI-Specification/registry/format/index.html

This is the part 1 of a series of PRs to address the formats.

[handrews]

Looks great! I reviewed all of the renderings and noticed that this fixed a bug in decimal where it was showing the issue number (again, as a non-link) instead of remarks. So this is already proving its value by fixing copy-paste bugs!