isFollowing = async (session, user) => {
  let is = await db.query(
    'SELECT COUNT(follow_id) AS is_following FROM follow_system WHERE follow_by=? AND follow_to=? LIMIT 1',
    [session, user]
  )
  return db.tf(is[0].is_following)
}
Returns whether session is following user
@param {Number} session Session ID
@param {Number} user User