Merge pull request slackapi#731 from seratch/v2.7.2-release

version 2.7.2

version 2.7.1

version 2.7.0

version 2.6.2

version 2.6.1

version 2.6.0

version 2.6.0rc2

Merge pull request slackapi#687 from seratch/v2.6.0rc1-release-note

Add v2.6.0rc1 release note

Merge pull request slackapi#578 from stevengill/master

2.5.0

2.4.0 (slackapi#572)