Support complex compound matches in Match criteria. For example, be able
to match against multiple Users for a given Match, or be able to match
against address ranges. Or Groups. Or any combination thereof.

Support for matching users can take one of several different appearances
in pillar data:

sshd_config:
  matches:
    match_1:
      type:
        User: one_user
      options:
        ChrootDirectory: /ex/%u
    match_2:
      type:
        User:
          - jim
          - bob
          - sally
      options:
        ChrootDirectory: /ex/%u
    match_3:
      type:
        User:
          jim: ~
          bob: ~
          sally: ~
      options:
        ChrootDirectory: /ex/%u

Note the syntax of match_3. By using empty dicts for each user, we can
leverage Salt's pillar mergine. If we use simple lists, we cannot do
this; Salt can't merge simple lists, because it doesn't know what order
they ought to be in.