Consolidate security sections in Hyper-Schema?

[handrews]

I find that having three big blobs of security discussion in the middle of the LDO definition makes it harder to follow what is going on.

Does anyone feel strongly about keeping them where they are, or can I just stuff them down as three subsections under a "Security Considerations" section? Such a section is definitely common in RFCs.

I would also add a cross-reference from the keywords with specific security concerns to the appropriate "Security Considerations" subsection.

[handrews]

Included in the rewrite work showing WIP with PR #427

[handrews]

Merged #427. This could still use work, but the contents of the merged section are what were there before so it's been re-organized as noted here and the specifics aren't worse than they were :-)