[cleanup] Use range for instead of std::for_each

See merge request !117

This commit replaces all use cases of std::for_each(..., std::mem_fn(...))
by a much more readble plain range for. It does not replace other uses,
where this may be more controversial.

[bugfix] correct Givens rotations after SIMD vectorization

See merge request !114

For SIMD vectorization, the branching in the Givens rotations was rewritten
using conditionals (which are vectorizable). Unfortunately, the branches for
cs and sn were mixed up during this step. This patch corrects the mathematical
behavior to the state before SIMD vectorization while retaining the vectorizable
conditionals.

Replace deprecated std functions

See merge request !115

The older variants for argument 1 or 2 were deprecated in C++11 and removed in
C++17, causing compilation failures with Clang 5 and libc++.

The former one was deprecated in C++11 and removed in C++17, causing
compilation failures on Clang 5 with libc++.

[bugfix] fix 'bildl_subtractBCT' for non 'FieldMatrix' matrices

Closes #35

See merge request !113

Incomplete LDL Decomposition

See merge request !104

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

Test whether vectors export 'reference' and 'const_reference'

See merge request !111

[feature][SeqILU] faster implementation of ILU preconditioner

See merge request !96

Implement the method 'setSize' for BDMatrix and BTDMatrix

See merge request !110

These are standard types from the STL.  Apparently all dune-istls
vectors do export them.

Test the method BCRSMatrix::setSize

See merge request !109

Implement construction of BDMatrix from std::initializer_list

See merge request !108

.gitlab-ci.yml: update environments

See merge request !106

resolve ambiguous call by explicitly calling `Dune::Hybrid::size`

See merge request !107

Reference: core/dune-common#77

- 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

[GeneralizedPCGSolver] Increment iteration counter for all verbosity levels

See merge request !105

This commit fixes Issue #32

kudos to Martin Nolte

default.

simple Compressed Row Storage for the lower and upper triangular
matrices. Also, SeqILU unifies both, SeqILU0 and SeqILUn.

[bugfix][cmake] install allocator.hh

See merge request !103