Fix wording and formatting of x0 special cases

[pfusik]

Restore semicolons removed accidentally in aaad788

[wmat]

Thanks for this, those semicolons somehow went missing. Can I suggest that you also change the "only valid" to "valid only", as it's grammatically an improvement.

[pfusik]

How about normalizing these "not equal" signs? Some are UTF-8, some are HTML entities and some are latexmath. I think UTF-8 would be best.

[wmat]

I think UTF-8 would work. Perhaps add attributes to the header docs for UTF-8 replacements, such as:

:le: ≤
:ge: ≥
:lt: <
:gt: >

Then replace in the asciidoc files with attribute references such as {ge}

[pfusik]

What do you mean by "header docs" ? Why use attribute references if we can (and already do) directly use Unicode characters? Especially for ASCII characters such as < and >.

[wmat]

Asciidoc requires header docs, for the ISA manuals, they are riscv-unprivileged.adoc and riscv-privileged.adoc. At the beginning of each is a set of attributes that asciidoctor requires to build the full documents. Adding attributes for unicode would but down on a few keystrokes for extension authors.

[pfusik]

I see, there's no ≠ on keyboards. But it was already extensively used and WYSIWYG. It's easier to copy the whole phrase than to re-type it. latexmath ended up in HTML as SVG - not good for screen readers.

[pfusik]

When merging, please select my Samsung email.

[aswaterman]

The title of this PR does not reflect what it actually does. It makes several wording changes.

[aswaterman]

Much improved, thank you.