Documentation format

We are working on updating the boost.org website, and when displaying the documentation of this boost library in that environment the display breaks due to the fact that ``s are used in the html. There will probably be a work-around, such as opening the docs in a new browser tab, but it would be preferable to either convert these docs to AsciiDoc as a modernization, or otherwise remove ``.

Start by inspecting the current documentation HTML as displayed on boost.org and identify where elements are used. Compare the proposed AsciiDoc modernization with removing frames or opening the documentation in a new tab; done requires an agreed approach and a verified display without the reported breakage.

索引モデルが issue の本文から書いたものです。