9.15.0-1

CHANGES:


Include the v9.15 Google OR-tools source and build together with the OCaml
interface. Rewrite the interface in C++ to avoid an unnecessary copy and
allow feasible solution observers.

Remove the eigen3 depext (this template library is now included directly in
the build). Adjust other dependencies based on recent work on conf-zlib
 and conf-bzip2.

Add Sat.Var.any.