v0.21.0 Handler groups & middleware

Overview

• Added HandlerGroup with ability to create new subgroups and apply middleware
• Added PanicRecovery middleware
• Added ToPtr helper func
• Fixed non ASCII chars in message entities

What's Changed

• Bump golang.org/x/text from 0.6.0 to 0.7.0 by @dependabot in #82

Full Changelog: v0.20.2...v0.21.0