Syntax: Formation [front|middle|back]
Formations allow groups to rank their members from front to back. Members
further back in the formation are less likely to be attacked, but members in
the back rank are also less able to attack hand to hand.
* The leader of the group must be in the front rank.
* Ranks behind the front must contain fewer group members than are in the
rank immediately in front of them. (Thus, the back rank can only be filled
with three in the front, and two in the middle.)