code: public static ClearableReference<Skill> createSkillMappingGetOld(Agent agent, Class<? extends Capacity> capacity, Skill skill) {
  		return agent.$mapCapacityGetOld(capacity, skill);
  	}
docs: Create the mapping between the capacity and the skill.
  
  <p>This function does not call {@link Skill#install()}.
  
  @param agent the agent.
  @param capacity the capacity to map.
  @param skill the skill to map.
  @return the mapping that is defined before the one created by the call to this function, or {@code null} if
  there is no previous mapping.
  @since 0.6
  @see #createSkillMapping(Agent, Class, Skill)