Tristan is considering buying shares in a company. Tristan asks you to explain to him what is meant by the terms 'member' and 'shareholder', and the different ways in which a person may become a member. He also asks you to explain who may be eligible to become a member, and how many members a company is permitted to have. Finally, Tristan asks: how does a person cease to be a member of a company? maximum 300 words