code: @Pure
  	public static <S extends Capacity> S getInternalSkill(Agent agent, Class<S> type) {
  		return agent.getSkill(type);
  	}
docs: Replies the internal skill of an agent.
  
  @param <S> the type of the capacity.
  @param agent the agent.
  @param type the type of the capacity.
  @return the skill.
  @throws UnimplementedCapacityException if the agent has not a skill for the given capacity.
  @since 0.6