// Medkits heal more with medicine skill.
pub fn treat(ctx) {
    if ctx.health() >= ctx.max_health() {
        ctx.message("You are not hurt.");
        return false;
    }
    let bonus = (ctx.skill_level("medicine") - 1) * 5;
    ctx.heal(ctx.item_prop("heal") + bonus);
    ctx.add_xp("medicine", 15);
    ctx.message("You patch yourself up.");
}