(docs) Finalized service page for a Puppet Server master

This page is a counterpart to the service information pages about the rack and
webrick masters. It will be displayed alongside them in the Puppet docs.
(docs) Fix glitchy or difficult Markdown formatting

Github's markdown will accept triple-backticks as code block delimiters,
but triple-tildes are more widely compatible. (Currently, the renderer
our docs site uses can't handle the triple-ticks.) This also cleans up
some nested lists to the least common denominator.