Add various events at critical moments to provide API windows

Problem/Motivation

While this module should provide common configurations that are applicable to most if not all Drupal sites, it is very likely that users will have unique needs that aren't a good fit for configuration.

Proposed resolution

Provide events for...

• Diff input alter
• Diff output alter
• Any others that are required

Remaining tasks

TBD

User interface changes

None

API changes

New events that end-users can listen for / react to.

Data model changes

None