Merge pull request didi#453 from didi/dev

1.设置版本为2.6.0; 2.补充v2.6.0的release notes

v2.6.0

Merge pull request didi#411 from didi/v2.5.0

升级到2.5版本

bump version to v2.4.2 and add release notes

bump version to v2.4.1

Merge pull request didi#252 from didi/dev_2.4.0

Dev 2.4.0

bump version to v2.3.1

Merge pull request didi#180 from didi/dev_2.3.0

Dev 2.3.0

Merge pull request didi#134 from didi/dev_2.2.0

merge dev 2.2.0

bump version to 2.1.0