ankane/groupdate — pull request #53 by trestrantham (2014-07-16 20:38:50+00:00)
Title: Add group_calc to enable custom calculations

This is an update to #47 that uses the latest groupdate refactor in an effort to simplify the interface for the user. The new DSL would be to use `group_calc` from a `Groupdate::Series`:

```ruby
User.group_by_month(:created_at).group_calc("(SUM(logins) / AVG(age))")
```