Send notifications when comments are created

Added a new interface - ICodeCommentChangeListener - to use for
notifications.

Added a new component - CodeCommentSystem - to act as the extension
point for the above interface. (This could have been added to one of the
other components, but I have plans for other refactorings and wanted a
clean base for them.)

Extended Comments.create() to trigger comment_created events.

Added a new component - CodeCommentChangeListener - to respond to
comment_created events.

Sub-classed trac.notification.NotifyEmail to generate notification
emails. Notifications are sent to the author of the resouce being
commented on, and anyone else who has commented on the same resource.
There is additional logic to determine who the notification should be
*sent* and *copied* to.

Added an option to control whether notifications are sent to the person
making the comment (off by default).

Removed unused variable.
Resolved #36 by providing instructions for building an egg locally.
Added notifications to README.
Extracted method to get real name from notify method.
Override NotifyEmail.send() so we can provide the from_name

No more swapping around of config values.
Removed entrypoints; using __init__ instead.
Clarified debug message for notification recipients.
Determine link to comment outside of template.
Removed superfluous debug logging of notification recipients.
Moved notification of change_listeners to a method on CodeCommentSystem
Moved logic for urls in notifications.
Handle email server being unavailable when sending notifications.
Merge pull request #42 from schwuk/notifications

Send notifications when comments are created

For now send them only to other participants of the thread, but this builds some infrastructure for sending them to more users.