reduce module dependencies

See merge request extensions/dune-vtk!3

replace explicit url in gitlab-ci.yml by internal includes

See merge request extensions/dune-vtk!4

Added data reader to VtkReader and a grid-function representation of the read data

See merge request iwr/dune-vtk!24

remove the central forward declaration

See merge request spraetor/dune-vtk!32

Error handling

See merge request spraetor/dune-vtk!31

remove some unused_variable and integer comparison warnings

See merge request spraetor/dune-vtk!30

make an explicit cast to field type for shape-function values

See merge request spraetor/dune-vtk!29

make an explicit cast to field type for shape-function values to allow float128 ctype grids. Note: the problem is that the runtime-order lagrange finite-elements do not support different range-type than double internally.

Refactoring/namespace changes

See merge request spraetor/dune-vtk!28

read cell offset and connectivity with flexible index type

See merge request spraetor/dune-vtk!25

replace Dune::Std::optional with std::optional

See merge request spraetor/dune-vtk!23

Remove LagrangeLFECache since it is not used anywhere in dune-vtk

See merge request spraetor/dune-vtk!22

lagrange data-collector for vtu files with entities of different dimension now ignores the lower dimensional entities