New sections are added: PAM options, crypttab options, commandline
options, miscellaneous. The last category will be used for all
untagged <varname> elements.
Commandline options sections is meant to be a developer tool: when
adding an option it is sometimes useful to be able to check if
similarly named options exist elsewhere.
https://bugs.freedesktop.org/show_bug.cgi?id=55890
Fixed typos, serial comma, and removed "either" as there were more
than two options. Also did an extra rename of "system-shutdown"
to "systemd-shutdown" that was forgotten in commit
8bd3b8620c
