* 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.

* 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.

improved spike chain generation in minapp

- improve robustness of time step and time integration
  interval selection
- changes of the type `if (!id)` to `if (id==0)`.
- fix bug selecting source cell gid when generating
  network connections
- make all-to-all network a user-specified option
    - updated README
- fix bug where an initial spike was not generated for
  the first cell on a communicator when the cell gid
  was a multiple of 20

Defines a TRACE(...) macro that, when enabled at
compile time with -DWITH_TRACE, prints to std::cerr
the location in the source, a time stamp, and the
values of any variables given to the macro.

Uses a mutex to protect against simultaneous writes
to std::cerr when TBB is enabled; it is not
optimized for speed.

Fixed small conflict and fixed compiler warnings about signed-unsigned
comparison when compiling in debug mode.

Conflicts:
	src/fvm_cell.hpp