Cast an Elixir Date.Range struct to cast into a DateRange

[schnittchen]

It would be great if

import Ecto.Query
alias PgRanges.DateRange
alias MyApp.Repo

range = Date.range(~D[2018-11-01], ~D[2019-01-01])

Repo.all(
  from e in Employee,
  where: fragment("? @> ?", e.employed_dates, type(^range, DateRange))
)

would be possible.

This is the same as in the Readme, just with a Date.Range struct in place of a PgRanges.DateRange struct.