add change log to readme.
send sms to participants.
event change send sms test.
Merge pull request #388 from saberma/saberma/changelog

项目主页显示近两月变更记录.
fixed rspec error.
fixed rspec error.
validate the length of event change content.
add sms sponsor: tui3.com
disable submit if event change content length is more than 50.
Merge pull request #389 from saberma/saberma-feature/381-send-sms-notification

#381 变更通知可以发送短信
Merge pull request #391 from saberma/saberma/list-sponsors

感谢推立方提供短信赞助，页脚显示赞助商 Logo
update tui3 link.
Merge branch 'upstream_master'