* fix build errors in tests with TBB
* set default probe output to none in miniapp

* the user can specify one of {none,AVX,AVX2,KNL} as
  targets for vectorization
* if modcc is available in PATH it will be used, which
  makes cross compilation easier
* a new flag USE_OPTIMIZED_KERNELS can be set to
  generate optimized kernels from the modcc compiler
  (equivalent to adding -O flag to modcc)

* `nest::mc::threading::sort` is analogous to `std::sort`
    * when using TBB the `tbb::parallel_sort` is used
    * otherwise `std::sort` is used
* used to parallelise connection construction during setup
    * now all initialization and simulation is multi-threaded
* added a unit test

* replace a call to `std::iota` with a for loop because the Intel
compiler was optimizing out the `std::iota` call in a unit test.
* add uniform syntax for converting pointer+size and ArrayView+size
into an ArrayView to provide uniform method for accessing ranges
inside mechanisms with/without optimizations.

Ranges and views implementations.

* Makes EXPECTS() fail handler a global, settable function pointer.
* Fix `util::upto` for bidirectional iterators with begin==end.
* Use `std::string` in error reporting with `either` in `partition_view`
  to correct incorrect default conversion in return value.
* Correct return types for `util::range::operator[]` and `util::range::at()`
* `transform_iterator` requires only iterator==sentinel test for correct sentinel
  behaviour.
* Extend partition tests to cover:
  * partition views over short (length) sequences,
  * non-numeric partitions,
  * throw on validation check of non-monotonic sequence,
  * make_partition with short and long size sequences, short division containers.
* Extend range tests to cover:
  * compatibility with `std::accumulate`,
  * correct constness of dereferences with respect to wrapped iterators,
  * proper type deduction for `make_range` over pointers.
* Extend span tests to cover:
  * span creation from `std::pair`,
  * proper type promotion with heterogeneous bounds.

* Adds non-owning range class describing a half-open interval
  by a pair of iterators, or by a start iterator and sentinel.
  (Assumption is that these are bounded ranges; unbounded
  ranges are on the todo list.)
* Adds spans and counting iterators, for iterating across
  intervals of integral types with a range-like interface.
* Partition in-place creation functions and partition views
  over monotonically increasing sequences.
* Two-field variant type implementation `util::either<A, B>`.
  (Used to provide an STL- and range for-loop accessible
  façade to sentinel-terminated ranges.)
* Some simplifications of utitliy classes and tidying up
  of formatting.

Global and Local spike exchange streamline

Exporter fixes

* single file per rank output creates one file per rank
* global file output creates one file only from rank 0

* MPI ranks now test the file that they generate, not that rank 0
generates
* code formatting updates
* added interface for getting file file name used by exporter

* single flag -f that turns output on (off by default)
* other parameters have to be provided by an input file
    * if -f is set the defaults will be used

Exporter fixes

Feature/exporter spike file

- sorting of includes
- bracket location
- all arguments on the same hight
- use of auto in the performance/io/disk_io.cpp

Do some small textual changes

fix importing of file export parameters from json

Rename exporter_interface
Move exportor to io directory

Merge branch 'master' of https://github.com/eth-cscs/cell_algorithms into feature/exporter_spike_file

Improve miniapp command line argument handling

* Resolves some conflicts.

Add 'nop_function' helper for trivial functions.

* Reformat some line breaks.
* Remove blank lines after comments.
* Reword/improve some comments.
* Explain what CustomCmdLine does in more detail.
* Remove vestigial declaration of 'args' in
  `CustomCmdLine::reorder_arguments()`