登录和用户名切换

登录右上角显示用户信息或者登录

            <div class="right-part">
                <div v-if="!token">
                    <span @click="put_login">登录</span>
                    <span class="line">|</span>
                    <span @click="put_register">注册</span>
                </div>
                <div v-else>
                    <span>{{ username }}</span>
                    <span class="line">|</span>
                    <span @click="logout">注销</span>
                </div>
            </div>