New message builder and bug fixes

Fixing slackapi#422

Bumping version so we can redistribute the package without the deprec…

…ated files. (slackapi#409)

Slack Python SDK v2.0 Official Release

Slack Python SDK v2.0 Beta Release

Version 1.3.1

1.3.0

Added rate limit handling for rtm connections

- You can now tell the RTM client to automatically reconnect by passi…

…ng `auto_reconnect=True`

Version 1.1.3

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