The HTML linter 'tidy' reports:

	go_spec.html:2556: Warning: unescaped & which should be written as &
	go_spec.html:3293: Warning: unescaped & or unknown entity "&s1"
	go_spec.html:3293: Warning: unescaped & or unknown entity "&a"
	go_spec.html:3294: Warning: unescaped & or unknown entity "&s2"
	go_spec.html:3294: Warning: unescaped & or unknown entity "&a"
	go_spec.html:2045: Warning: trimming empty <p>
	go_spec.html:4526: Warning: trimming empty <ul>
	go_spec.html:4533: Warning: trimming empty <ul>
	go_spec.html:4539: Warning: trimming empty <ul>

This CL fixes all but the <ul> ones, which I think should be fixed
but are defended by a comment.

Change-Id: I0ca88f5e80755024801877ab1298025ecf8f10c5
Reviewed-on: https://go-review.googlesource.com/c/go/+/214457Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>