Ortools

Dependency Updates
* abseil-cpp 20200923.2 -> 20200923.3
* Protobuf 3.14.0 -> 3.15.3

Routing
* Expose new APIs:
* `int RegisterUnaryTransitVector(std::vector<int64>)` and
* `int RegisterTransitMatrix(std::vector<std::vector<int64>>)`
* Change return of `AddVectorDimension()` and `AddMatrixDimension()` to `std::pair<int, bool>` whose `int` is the transit evaluator id.

Dependency Updates
* abseil-cpp 20200923 -> 20200923.2
* Protobuf 3.13.0 -> 3.14.0
* Add support for Gurobi 9.1.0
* drop Glog dependency (replaced by a custom implementation depending on abseil-cpp flags)
* drop Gflag dependency (replaced by abseil-cpp flags component)

Bug Fixes
* Fix double counting of Gurobi floating license (2227)
* Fix windows build (2200)

Dependency updates
* abseil-cpp 20200225.2 -> 20200923
* Protobuf 3.12.2 -> 3.13.0

Platform changes
* Added support for Python3.9 (2187)
* Dropped support for Python3.5 (2186)
* Added support for Ubuntu 20.10 (2188)
* Dropped support for Ubuntu 16.04 LTS and Ubuntu 19.10 (2188)

Known Breaking Change
* Since last synchronization with Google internal code base, now Routing and SAT (i.e. OR-Tools) use some **C++17**.
**WARNING**: If you provide your own version of **abseil-cpp** please verify it is built against **C++17** too.
* The `MPSolver::CreateSolver` signature has been changed. The model name argument has been dropped.

CMake
* Fix disabling SCIP support when using `-DUSE_SCIP=OFF` (2129)
* Integrate samples and examples to the CMake build system.
note: can be disable by using `-DBUILD_SAMPLES=OFF` and `-DBUILD_EXAMPLES=OFF`.
note: can be disable for a specific language using `-DBUILD_<LANG>_SAMPLES=OFF` or
`-DBUILD_<LANG>_EXAMPLES=OFF` (with `<LANG>` among `CXX`, `PYTHON`, `JAVA` and `DOTNET`).

Make
* Require `Make >= 4.3` (use of Make [eval function](https://www.gnu.org/software/make/manual/html_node/Eval-Function.html)).
* Require `CMake >= 3.14` (use of CMake [`--verbose`](https://cmake.org/cmake/help/v3.14/manual/cmake.1.html#build-a-project) option).
* Add option to disable SCIP support using `USE_SCIP=OFF` (2134)
* Add option to disable CLP and CBC support using `USE_COINOR=OFF`

Java
* OR-Tools now generate maven packages (202).

Bug fixes
* Fix C++ and Python build on FreeBSD (2126).
* Fix build in debug on windows (2077).
* Fix long standing crash in parallel on CP-SAT on Windows (2001, 2019).

Dependency updates
* Gurobi 9.0.2 is now pre-integrated in prebuilt binaries. It will search for the gurobi 90 shared library in the default install path of the Gurobi installers on MAC OS X and Windows, or in the `GUROBI_HOME` directory.
* SCIP 7.0.1 is now integrated in prebuilt binaries.Please ensure compliance with the [SCIP license](https://scipopt.org/index.php#license) before using it.
* Added support for optional Xpress Solver 8.9.0.

Linear Solver
* Added a static `LinearSolver::CreateSolver()` method to simplify checking support for integrated linear solver backends. It works in all languages.

CMake
* Fix and add support for FreeBSD (2105)
* Use of `FetchContent()` to build dependencies
* Use of CMP0091 to control Runtime Library on Windows

Bazel
* Cleanup protobuf usage.

Bug fixes
* CP-SAT: Fix sorting in cumulative cut generation.
* Linear Solver: Fix leak in .Net wrapper when using `CreateSolver()`.

Dependency updates
* Abseil-cpp 20200225 -> 20200225.2
* Protobuf 3.11.4 -> 3.12.2
* bazel-skylib 0.8.0 -> 1.0.2 (for bazel based build)
* Fix optional SCIP 7.0 support

CP-SAT Update
* Now, the solver returns Optimal instead of Feasible in a satisfiability model (i.e. without objective)
* Fix multi-threading crash (2005)
* Improve feasibility pump

CMake
* Add maven package generation (202)
* Fix Windows build

Dependency updates
* Abseil-cpp 8ba96a8 -> b832dce (LTS 20200225)

CP-SAT Update
* Improve cut management
* Add debugging tools
* Fix UNSAT bug in presolve (see 1908)

Bug fixes
* Fix swigwin.exe url
* Fix swig typemap management for Java and .Net