Remove old exercise
Basic one-to-many association
Remove MVC for this first exercise
Remove old validation exercise
Validation exercise
Fix URL
Fix spec
Regex validation
Add some reference to callbacks
Refine test for callback
Fix test
Free sinatra exercise
Remove HN MVC end in profit of Sinatra app
Merge branch 'master' of github.com:lewagon/promo-4-challenges
migrate and seed