Editing after review

[felixlinker]

With this PR I address my comments on editing in this review: https://mailarchive.ietf.org/arch/msg/cose/b7ZLpC3U5CNhQscCi6ErDvFk9kg/

Some reasoning.

• I replaced the terms "latest" and "previous" with "newer" and "older." This is in-line with RFC 9126 and emphasizes that consistency proofs about the past can be generated.
• I fixed what I believed to be errors at the beginning of 5.2.1. There, it said "previous" root (I believe correct would be just any root you wish to prove inclusion for) and "tree-size-1" (which I believe should be "tree-size").
• I removed an ambiguous occurrence of the word "signature." I think the text is clearer without it.

[robinbryce]

I also believe it should be possible for a consistency proof to show consistency between two arbitrary points in the log. So the 'older' / 'newer' frazing seems like an improvement to me also

[OR13]

I think the first sentence could be clearer, but the rest of these changes are improvements.

[SteveLasker]

LGTM, with, or without the nit suggestion at line 302