anchor.diff:  Returns the unique *id* of the group.
   
   
  -=== Instance methods
  -
  -==== addMember(User $user) : void
  -
  -Adds '$user' to the group in the database.
  -
  -
  -==== getMembers() : array
  -
  -Returns an array of *User* objects representing the group's members.
  -
  -
  -==== containsMember(User $user) : bool
  -
  -Returns *true* if group contains '$user', otherwise *false*.
  -
  -
  -==== removeMember(User $user) : void
  -
  -Removes '$user' from the group in the database.
  -
  -
  -==== remove() : void
  -
  -Removes the group from the database.
  -
  -
  -=== Static methods
  +=== Group Management
   
   ==== __construct(int $id)
   
  
positive.code: 
  Returns an array of *Group* objects representing all groups which '$user' is a member of.
  
  
  ==== setupDB() : void
  
  
negative.code: for more details.
  
  
  ==== remove() : void
  
  Removes the group from the database.
  
  
  ==== getAll() : array
  
  Returns an array of *Group* objects representing all groups in the database.
  