now simulation time is stored as a class attribute of ParticleSystem.
eliminates 'tstep' attribute in integrator class. Also adds some improvements in hermite module.
improvements in nreg.
ParticleSystem has been simplified and improved. Now __getattr__/__setattr__ methods aren't needed anymore and as a consequence the overall performance of execution has been improved.
now rebinding attrs in ParticleSystem class is more efficient than previous implementation. Also, adds some improvements in other modules.