Log message:
Update ocaml-typerep to 112.17.00.

- Split out typerep_extended which is now using core_kernel

Log message:
Add OCaml library typerep into wip/ocaml-typerep.

This library defines a syntax extension for OCaml using Camlp4 that
can be used to define first class values representing record fields,
and additional routines, to get and set record fields, iterate and
fold over all fields of a record and create new record values.