The latter is the standard name for it and it is hidden from the
generated documentation of the public interface.

The algorithms are supposed to be used via overloaded plain functions in
the Algorithms namespace: for now, there are only inplaceInclusiveScan
and inplaceExclusiveScan (and their distributed variant).

The scan and segmentedScan methods were removed from data structures
(Vector, VectorView, DistributedVector, DistributedVectorView). They
were inflexible (only std::plus was actually used for reduction),
incomplete (some overloads just threw NotImplementedError), and they
were violating the open-closed principle:
https://en.wikipedia.org/wiki/Open%E2%80%93closed_principle

Also moved the test under Algorithms and made sure it is actually
being compiled.

The first phase performs only per-block reduction, not scan. The output
array elements are written only in the second phase, so overall we
perform only `n` instead of `2n` write operations.

Also fixed the idempotent values for Max and MaxWithArg
(std::numerical_limits<T>::lowest() vs std::numerical_limits<T>::min())

Hence, all StaticArray, Array, ArrayView and even expression templates are
directly usable in reduction without the need to create a wrapping fetch
functor. Also NDArray has this interface in 1D.

The tests should not rely on other parts of the library if possible.

- sequential scan does not need to be split, so "perform" performs the
  whole simple scan algorithm, "performFirstPhase" only reduces the
  block (i.e. the whole vector), "performSecondPhase" performs the scan
  operation with the block result combined with a global offset as the
  initial value
- parallel OpenMP scan calls the sequential scan to process the block
  results
- parallel CUDA scan was changed such that the block results array is an
  exclusive scan after the first phase, same as in the other device
  specializations

- used ValueType instead of RealType - closes #87
- replaced prefix-sum with scan in the comments
- renamed variables containing "sum" to "result"
- fixed artificial blockShifts in the sequential implementation

The file should be named after the main function which is implemented in
it. Also changed the parameter name from "reduce" to "reduction" to
differentiate it from the main "reduce" function.

extension of the implementation of staticFor

See merge request !95

This reverts commit 05859cdd.

To/sorting

See merge request !99

Fixing header including in Nvidia bitonic sort wrapper.

Fixing namespaces definition.