* Clean up validation CMake
* Use configure-time path to validation data by default
* Checks in validation data
* Bring validate_synapses up to date with current source API.
* Allow -p option in validation test to point to validation
  data directory.

* Add a tweaked version of exp2syn.mod that is modparser compatible.
* Add option to simple_synapse.py to choose which syn type to use.
* Compatibility tweak for runinng nrn scripts with nrniv -python

Feature/plotting

* Use `units` consistently in miniapp.cpp
* Describe the special treatment of the metadata key
  `label` in tsplot.

* Adds README.md for scripts (currently just for tsplot)
* Renames tsplot.py to just tsplot for simplicity
* Change long option --out to --output for tsplot

* Do not try to plot excluded points if there is no
  excluded time series to plot.
* Perform runtime check on matplotlib version for early
  exit in case of mismatch.

further style fixes in point

* Add -x option to clip extreme y values automatically.

Unicode handling changes between 2.7.9 and 2.7.12, and
what worked transparently in the latter breaks weirdly
in the former. This patch coerces everything to unicode
for great justice.

Fix logger warning issue.

First working implementation.

* miniapp saves more metadata in json output, including units
* tsplot.py will plot multiple timeseries, optionally gathering
  multiple plots on the one axis set

Note that documentation is missing and there isn't a clipping
functionality in tsplot.py, which it should have in the presence
of numerical instability.

fix cmake to find TBB installed from source

there was a problem with the FindTBB script for cmake where it cmake was
not looking in paths specified by the environment variable LIBRARY_PATH,
which meant that it was not finding the TBB library files when TBB had
been installed from source and configured with tbbvars.sh

Address gcc 6.1 warnings

add missing cmath header

GCC 6.1 was unable to find cmath in src/point.hpp

Feature/refactor tests directory

Adapt sources to include test_unit.hpp
Add empty CMakeLists.txt to all test type directories

Gtest is currently copy twice!

Fix optional<X&> assignment.

* Correct implementation of operator=().
* Unit test for optional reference assignment.

Modifications to util::optional for KNL compilation

Turn off warning about unused template parameter, when the
parameter is used for SFINAE tests inside the template
parameter list in the json library.

The Intel compiler was unable to compile the
`util::optional` code, and also created some warnings
in the unit tests for optional
* rephrase `enable_if` template argument to use `::value`
  explicitly to work around Intel compiler bug.
* move helper types out of anonymous namespaces in the
  optional unit tests
    * fix warnings about unused member functions
* remove some white space in optional code

rename cl_options.check -> check_and_normalize

Feature/debug trace

* Add `multithreaded()` constexpr function in threading
  namespace.
* Replace `WITH_TBB`-guarded code with multithreadedness-
  checking code.