doc: update manpage, mention -A and annotation rows
Extend the manpage section which documents the -A option to select
annotation output. Mention that rows are supported in addition to
classes.
Rephrase the paragraph about multiple decoder specs in a single -A
option. Each of them can select multiple annotation classes, while the
previous documentation strongly suggested that only one class would be
available. [ best viewed with 'git diff -U10' ]