Add migration for discussions
Add Discussion module
Setup errors and defaults for Discussion
Add validation for discussion ids
Add Comment module
Fix target_type column in discussions migration
Cleanup docs for user constructor
Add .equals() for comments and discussions
Add .getDiscussionsFor(), .addDiscussion() to storage
Upgrade should to 2.1.0
Set defaults for discussion.createdAt, .updatedAt
Change Discussions.updated_at to `NOT NULL`
Simplify construction and clearAll() of local storage
Add Storage#addComment(), #getComments()

Add .addComment(), .getComments() to storage
Add Storage#getDiscussions()
Return id from Storage#addDiscussion()
Only validate discussion target owner if set
Set target owner for stored discussions
Add Comments and Discussions modules
Only set default comment date if unspecified