v0.13.0

This release introduces some backward-incompatible changes. Before upgrading,
please review these notes.

• Type resolution has been refactored to allow assembling query fragments based
  on the type information.

• Type checking is now more strict. A Define field or an optional Join will
  be validated even when they are to be elided.

• Resolution of ambiguous column names in Join has been changed in favor of
  the right branch. Previously, an ambiguous name would cause an error.

• Node-bound references are no longer supported. The following query will
  fail:

  qₚ = From(:person)
  qₗ = From(:location)
  q = qₚ |>
      Join(qₗ, on = qₚ.location_id .== qₗ.location_id) |>
      Select(qₚ.person_id, qₗ.state)

  Use nested references instead:

  q = @funsql begin
      from(person)
      join(
          location => from(location),
          location_id == location.location_id)
      select(person_id, location.state)
  end