Build and export Google OR-Tools models

Google OR-Tools is an open source software suite for optimization, tuned for tackling the world's toughest problems in vehicle routing, flows, integer and linear programming, and constraint programming. This package provides OCaml functions for working with the Protocol Buffer formats that are read and written by the different solvers. It does not actually depend on the OR-Tools software, which need not even be installed. The interface currently only supports a subset of the features provided by the CP-SAT solver. Pull requests for more features and solvers are welcome.