Class-based plugins

[archangelic]

Implement class-based plugins for all features going forward.

Spec for class-based plugins:

• [x] ability to give help info back to bot
• [x] abstract way to send message to calling channel or other channel without returning
• [ ] multiple command and listener support in single class (via method decorators)
• [ ] on_mention decorator
• [ ] cmd and listener plugins should meet these specs
• [ ] ability to inform bot of aliases for commands
• [ ] editable settings (possible work on bot to get this working)

[ixxie]

Some of the considerations outlined in https://github.com/archangelic/pinhook/pull/60 could be considered when developing class-based plugins.

[archangelic]

As of 1.8.0, this is in alpha and features of class-based plugins might change significantly.