Ortools

Fix Protobuf version on UNIX: ~v3.1.0-alpha-1 (3d9d1a1255) -> v3.5.1

Update to required dependencies
* Protobuf 3.5.0 -> 3.5.1

Misc
* Refactor base to prepare abseil-cpp integration.
* Add some CI jobs.
* Add `make install_python` target.
* Use `JAVA_HOME` instead of `JDK_DIRECTORY`

SAT
* Performance improvement.
* Improves Python API.
* Add C API aka CpSolver.cs (EXPERIMENTAL).

Glop
* Code refactoring.
* Performance improvement.

CMake Support (EXPERIMENTAL)
* Add C++ OR-Tools CMake support.
* Be able to build OR-Tools as a standalone CMake project.
* Be able to incorporate OR-Tools into an Existing CMake project.
* Add Python OR-Tools CMake based build.
* Generate python package (wheel) using CMake.

Contributions
* Fix winsock2.h redefinition on windows Thanks to <a href="https://github.com/darkengines">Florent Tollin de Rivarol</a>.
* Add F Support (EXPERIMENTAL) Thanks to <a href="https://github.com/acco32">Matthew Moore</a>.
Note: only available with Makefile builder.
* Add .NET Standard Support (EXPERIMENTAL) Thanks to <a href="https://github.com/DevNamedZed">Ziad Elmalki</a>.
Note: only available with Makefile builder

Full list of commits since v6.6 [here](https://github.com/google/or-tools/compare/v6.6...v6.7)

Updates to required dependencies
* Protobuf to 3.3.0 -> 3.5.0.
* gflags to 2.2.0 -> 2.2.1.
* CBC 2.9.8 -> 2.9.9.
* Add Python module six (1.10) as required dependency for Python.

Bugfixes
* Pull request 494 Name refactoring. Adding comments for IntelliSense in some editors.
Thanks to <a href="https://github.com/acco32">Matthew Moore</a>.
* Pull request 516 Instruction for F standalone binary.
Thanks to <a href="https://github.com/acco32">Matthew Moore</a>.
* Improve precision in Glop.

SAT Solver
* Improve internal SAT solver, Fix various bugs.
* Add a VRP constraint to the SAT solver, linked to the LP solver.
* Change the solution observer in the SAT solver to take a CpSolverResponse as a parameter.
* Improve the use of Glop in SAT Solver.
* Speedup SAT-LP connection.</li>
* Add Reservoir constraint to the SAT cp_model protobuf format.

SAT/Python
* Introduction of the SAT API in Python.
* Code in <a href="https://github.com/google/or-tools/blob/master/ortools/sat/python/cp_model.py">ortools/sat/python/cp_model.py</a>.
* Add examples in <a href="https://github.com/google/or-tools/tree/master/examples/python">examples/python/</a>:
* <a href="https://github.com/google/or-tools/tree/master/examples/python/assignment_sat.py">assignement_sat.py</a>
* <a href="https://github.com/google/or-tools/tree/master/examples/python/assignment_with_constraints_sat.py">assignment_with_constraints_sat.py</a>
* <a href="https://github.com/google/or-tools/tree/master/examples/python/code_samples_sat.py">code_samples_sat.py</a>
* <a href="https://github.com/google/or-tools/tree/master/examples/python/cp_is_fun_sat.py">cp_is_fun_sat.py</a>
* <a href="https://github.com/google/or-tools/tree/master/examples/python/gate_scheduling_sat.py">gate_scheduling_sat.py</a>
* <a href="https://github.com/google/or-tools/tree/master/examples/python/hidato_sat.py">hidato_sat.py</a>
* <a href="https://github.com/google/or-tools/tree/master/examples/python/jobshop_ft06_sat.py">jobshop_ft06_sat.py</a>
* <a href="https://github.com/google/or-tools/tree/master/examples/python/nqueens_sat.py">nqueens_sat.py</a>
* <a href="https://github.com/google/or-tools/tree/master/examples/python/nurses_sat.py">nurses_sat.py</a>
* <a href="https://github.com/google/or-tools/tree/master/examples/python/rcpsp_sat.py">rcpsp_sat.py</a>
* <a href="https://github.com/google/or-tools/tree/master/examples/python/steel_mill_slab_sat.py">steel_mill_slab_sat.py</a>
* <a href="https://github.com/google/or-tools/tree/master/examples/python/worker_schedule_sat.py">worker_schedule_sat.py</a>

* Add support for <a href="https://github.com/google/or-tools/blob/master/examples/notebook/README.md">IPython notebook.</a>
* Python examples are exported to notebooks and available in <a href="https://github.com/google/or-tools/tree/master/examples/notebook">examples/notebook</a>.

Examples
* Rewrite <a href="https://github.com/google/or-tools/tree/master/ortools/data/rcpsp_parser.h">rcpsp_parser</a> to use ProtoBuf format to store the problem.
* Improve RCPSP parser.

Full list of commits since v6.5 [here](https://github.com/google/or-tools/compare/v6.5...v6.6)

Change in platforms

- Pypi modules on Linux platforms are now delivered as wheel files using the manylinux1 tag. Thanks to Federico Ficarelli. With this change, we have backtracked the per-linux modules introduced in the July 2017 release.

New features

- Improved scaling method used inside GLOP.
- Fix wrapping of evaluators in the C routing library. Thanks to DevNamedZed.
- Improve the performance of the flatzinc presolve for large models.
- Use the SAT backed for flatzinc by default.
- Improve performance of the Core based approach for the sat solver.
- Fix bug in the linear assignment algorithm that was failing incorrectly.
- Added F examples in ortools/examples/fsharp. (Thanks to Matthew Moore).
- Remove check for positive penalties in the routing library.