`address` and `port` description were being rendered as bold because of
an extra space indenting its `required` note.
Also escaped `true`/`false` terms for the `persistent` option.
Add username and password settings to the APT Proxy plugin so that
users who are behind an authenticating proxy can still use bootstrap-vz
without having to jump through hoops. If either the username or password
are not set, then no authentication is used.
This is the first step in the effort of combining all documentation about
bootstrap-vz into sphinx while still being able to access it from github
(github can parse rst as well)
