Add or-tools support

[danoliv]

We have been successfully using Optimus with or-tools as well in one of our projects.

At the moment we are using a small wrapper with the added functionality but I think that other people could benefit from this.

If you agree with this I would like to open a MR so we can merge the updates on the main project.

Thanks

[vagmcs]

Sounds good. Feel free to prepare an MR.