[cleanup][Python] Remove debug print statement.

See merge request !245

[feature][Python] Compile commonly used reference elements into Python module.

See merge request !244

submodules.

dune-geometry Python module to avoid code generation.

Add a Mapping of a Geometry

See merge request !192

Align leftInvA with rightInvA

See merge request !242

[cleanup] Stop using deprecated header keywords.hh

See merge request !240

This is a pure whitespace change, separated from the rest
to improve readability.

* Replace macro `DUNE_INLINE_VARIABLE` by `inline`,
  because for the supported compilers it's always defined to this way.
* Stop including deprecated, no longer used header `keywords.hh`.
* Remove conditionally defined anonymous namespace,
  because for the supported compilers the condition always evaluates
  to false.

[cleanup 2] Remove warning about index access out of bounds.

See merge request !239

[cleanup] Remove warning about index access out of bounds.

Closes #35

See merge request !236

Remove code deprecated in Dune 2.9

See merge request !237

Fix Doxygen warnings

See merge request !235

Probably a left-over from the split from dune-grid

This is uncommon in Dune.
Doxygen does not like them.

Found by Doxygen.

Remove argument from cmake command finalize_dune_project

See merge request !234

Default constructible geometries

See merge request !224

[cleanup] Remove workaround for issue 19 as GCC 8.2 was dropped

See merge request !227

The code works around an issue with a bug in GCC 8.2. As we
require GCC 9 or newer, this is no longer needed.

Incrase minimal required CMake version to 3.16

See merge request !226

CMP0087 is set to NEW since CMake 3.14.