And fix all spelling errors that codespell currently finds.

See https://reuse.software/ for a description.

fix ci

pep 42: use implicit namespace packages which make it possible to combine subpackages using editable (source) and non editable (pypi)

only use a cmake install a python module in the SKBUILD setting - for an install from build dir pip will take take of this since it is part of the setup.py file

add a stopgap solution unti ci repo up and running again

Update requirements.

add dune packages to requires in setup.py.in

[testing]

only add dune modules that have been found as requirements in setup.py.in

removed setup.py.in since the default is provided in dune-common

adapt ci yml file to python bindings on by default

disable python bindings for clang 5 (ubuntu 18) since no numpy matching numpy version can be installed from the gitlab registry

[bug fix python bindings]
fix an issue with 'entry' being used in implicit build mode but ready==build

This is a workaround for a bug that showed up after gitlab migration. See issue
infrastructure/issues0#62 for further discussion.

Suitesparse, as installed with Debian, is thread-parallel using OpenMP.
OpenMP silently assumes, it can spawn as many threads as there are cores.
In a worst case scenario, this leads to a number of threads quadratic in
the core count, if you also do parallel test execution with the maximum
number of cores. We solve the issue by disallowing OpenMP to allocate more
than one thread.

This way dependencies installed via `duneci-install-module` are built
with the same options as the module to be tested.

- Added:   Debian 10 with gcc in C++17 mode
- Removed: Debian 8 + Backports with clang

Reference: http://lists.dune-project.org/pipermail/dune-devel/2017-July/002224.html

- No longer test with clang 3.5.
- Add clang 3.8 from Debian 8 + backports
- Add gcc 5.4 + clang 3.8 from Ubuntu 16.04 LTS.
- Use `duneci-standard-test`