TNL compiles with MPI by default.

Conflicts:
	src/TNL/Solvers/MeshTypeResolver.h
	src/TNL/Solvers/MeshTypeResolver_impl.h
	src/TNL/Solvers/PDE/TimeDependentPDESolver_impl.h
	src/TNL/Solvers/SolverInitiator.h
	src/TNL/Solvers/SolverInitiator_impl.h

Conflicts:
	CMakeLists.txt
	src/TNL/Meshes/CMakeLists.txt
	src/UnitTests/CMakeLists.txt

This version should compute same results if distributed or not distributed.

Conflicts:
	src/TNL/Meshes/DistributedMeshes/DistributedGridIO.h
	src/Tools/tnl-init.h
	src/UnitTests/Mpi/DistributedGridIOTest.h
	tests/mpi/CMakeLists.txt

Conflicts:
	src/TNL/Problems/HeatEquationProblem_impl.h
	src/TNL/Solvers/PDE/ExplicitUpdater.h

* origin/mesh: (251 commits)
  Updated CMakeLists.txt files for meshes
  Added missing __cuda_callable__ flag to MeshEntity
  Fixed comparison between signed and unsigned
  Optimizing mesh initializer, replaced EntitySeedKey with EntitySeedHash
  Added timer to MeshReaderTest
  Fixed SubentityAccessLayer
  Fixed typo in mesh StorageLayer
  Removed checkCells method from the mesh initializer
  Switched static functions to inline
  Fixed comparison between signed and unsigned
  Fixed constness of reader in MeshTypeResolver
  Renamed VTKEntityType to EntityShape
  Renamed MeshConfigBase to DefaultConfig
  Removed static asserts from MeshConfigBase
  Fixed internal linkage of functions in VTKEntityType.h
  Added specialization of getEntityMeasure for quadrilaterals
  Simplified and generalized the getEntityCenter function
  Added getEntityCenter and getEntityMeasure functions
  Removed unused methods
  Removed GlobalIndexType and LocalIndexType from the public interface of MeshEntityTraits
  ...

* master:
  Documentation.

Python bindings

See merge request mmg/tnl-dev!2

Conflicts:
	src/TNL/Communicators/MpiCommunicator.h
	src/UnitTests/Mpi/DistributedGridIOTest.cpp

And of course our implementation is faster ;-)