Moved spike buffer to the manager. This allows reuse the by other registered exporters

Default is false
No output via command line parameters

Make the spikes have realistic id's and timings, the amount of chars to output is now more in line with
realworld output

Added a simple switch to select functionality
No correct file output name setting yet.

file per rank and file per simulation

Add unique _ptr to the model class (will be refactored later to have a manager)

Commit upstream changes

Bugfix: incorrect specialization

Some compilers are more liberal than others…

Pull in upstream patches to local copy

Command-line support for limitting trace output.

New options:
 * -p, --probe-ratio      Attach probes to this proportion of cells
 * -X, --probe-soma-only  Don't probe dendrites
 * -P, --trace-prefix     Specify where to write traces
                          (default: 'trace_')
 * -T, --trace-max-gid    Don't trace cells with a larger gid than this.

Fixes issue #40

The resulting trees are not equivalent to the initial ones. All
offending branches were split and their non-contiguous part was moved
directly below the root.

asynchronous communication and compute 

Pull in upstream patches to local branch

Feature/model refactor

* fixed const interface to the serial proxy for thread private storage
* added a serial proxy for tbb task group and moved the tbb task group
  behind the threading interface.
* added comments to the communicator to better document each method

- moved spike source storage to its own file
- added unit tests for spike storage

Merging for PR#64 review.

Address PR#64 review comments.

- communicator no longer accepts or stores thread-local spike buffers
- buffers and queues are stored and managed outside communicator
- a new type thread_private_spike_store that manages the thread
  private spike buffers

Feature/model+recipe

Regression test for bugfix in commit #712c00a7