Update time should have time as well as date.

Before this commit, update timestamp only contains dates.
But update timestamp should have times.
Install `sequel` gem.

see: http://qiita.com/futoase/items/9c76b2a50ba31f866f16
Add migration file for database table.

see also: http://qiita.com/futoase/items/9c76b2a50ba31f866f16
Rename `test.db` to `events.db`.
Delete `data` directory and delete its entry in .gitignore.
Use Ruby 2.0, instead of Ruby 1.9.
Refactor `Rakefile`.
Merge branch 'dev'