Removed reduction methods from Array and ArrayView, instead added overloads of reduce and reduceWithArgument for arrays/views

Plain functions are much more flexible than methods. The methods were
also violating the open-closed principle:
https://en.wikipedia.org/wiki/Open%E2%80%93closed_principle

This adds back the original approach (prescan + uniform shift) which
was removed too early.

The original approach (prescan + uniform shift) is more efficient for
inputs that are expensive to evaluate, such as vector expressions.

Using an odd number of valuesPerThread avoids shared memory bank
conflicts even without a special interleaving. We also save some shared
memory this way.

Small inputs can be scanned with just one CUDA block, which avoids the
scan of block results and second-phase kernel. Hence, large arrays can
be scanned with just 3 kernel launches instead of 4.

The input values are first copied into shared memory, reduced
sequentially across chunks, and scanned only at the end of the kernel.
This follows the upsweep-downsweep approach by Blelloch which is more
work-efficient. Also the distinction between exclusive and inclusive
scan appears only at the end of the kernel, which avoids the weird "+2"
size of the shared memory.

Also used Cuda::getInterleaving() for the indices when accessing the
chunkResults array, which avoids shared memory banks conflicts in the
spine-scan phase.

- input and output are passed by views rather than raw pointers (this
  allows to scan even vector expressions)
- consequently, indexing is different (begin and end for the global
  memory accesses)
- fixed calculation of currentSize in the launcher
- changed configuration of the kernel using the blockSize and
  valuesPerThread template parameters rather than the elementsInBlock
  runtime parameter
- changed allocation of the shared memory from dynamic to static
- the second phase kernel uses shared memory to cache block results for
  each block

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.