[refactor] Added 'authored_at' to commits (eventually to replace 'date')
[skip] Added validations to Commit
[fix] Rewrote repo.refresh! to perform a clone instead of a pull if need be
[refactor] Downcased the email addresses of committers
[improvement] Associated commits with their committers
[improvement] Added a job for syncing commits nightly
[skip] Refactored the migration for adding authored_at to commits