113.00.00

• Added Fields.Direct.set_all_mutable_fields, a function intended to
  guarantee when pooling records that one cannot forget to reinitialize some
  fields.

  Obviously one could achieve this through something like
  Fields.Direct.iter, but we want a more efficient version that
  doesn't force the call side to create closures.

109.19.00

• Made with fields generate the same functions in the Fields and
  Fields_of_* modules whether the type is called t or not.

109.14.00

• Made with fields expose first-class fields for private types while
  preserving privacy.

  There is now an additional phantom type in a first-class field that
  prevents building or modifying elements of a private type.

  One consequence of this change is that the Field.t type is now an
  abstract type -- it used to be exposed as a record type. So, one
  must, e.g., change field.Field.name to Field.name field.

109.12.00

• Added back Fields.fold to with fields for private types.

  We had removed Fields.fold for private types, but this caused
  some pain. So we're putting it back. At some point, we'll patch
  with fields to prevent setting mutable fields on private types via
  the fields provided by fold.

109.11.00

• with fields, for a type u that isn't named t, creates module
  Fields_of_u rather than module Fields. This allows one to us
  with fields on several types in the same structure.

109.10.00

• Changed with fields on private types to not expose mutators or
  creators.