Update interface with new methods and remove duplicated docs

[dpi]

Description

• interface updates: new methods, adds a variety of methods to the interface that have been added since the interface was introduced.
• Removed documentation from Pusher class. Documentation is implied when inherited from interface.

For the most part, this PR is just a bunch of move/copy-paste.

CHANGELOG

• [CHANGED] Added newly introduced methods to Pusher interface.

[GrahamCampbell]

This is a major breaking change.

[dpi]

Perhaps, do the maintainers of this project consider the missing methods from the interface intentional?

Should implementors of the interface be required to add these methods?

Other ideas:

• Wait for a new major
• Add new methods to interface as @method instead, at least in the interim.
• I think the doc removals from Pusher class could happen immediately.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If you'd like this issue to stay open please leave a comment indicating how this issue is affecting you. Thank you.