Collectively, these trigger warnings in both Doxygen and
clang (-Wdocumentation-unknown-command).  Weirdly, @p in doxygen doesn't do
anything but print in a fixed-width font anyway, so just use Markdown quotes to
replace it which has the same effect (and reads nicer in the source).  The use
of @param like @p was invalid, so do the same to those.