Created the Note plugin.

The Note plugin lets you add, show, list and delete notes. Notes are
stored in a local text file for later retrieval.
Updated the TODO file.

Added a TODO for listing available commands.
Created the Bugs plugin.

It initially enables accessing a Bugzilla instance for bug details.
Created the Helper plugin.

It allows plugins to register a help line that is then shown to the user
when they enter "!help".