Add the const keywork in front of local constant that have been added in the code. Also add the static-ordered
trick in the peek() function of the SynapticPathway, to share the load safely among threads. Even if not parallel,
this seems to be still a bit faster than one thread running everything. Did some profiling: performances are always
increased with OpenMP, as long as the defaultclock is not too small. Sadly, for code using small dt (<0.1ms), the overhead due
to loops and to synchronization slows everything compared to without OpenMP