Improve docstrings for IIR in ProportionalIntegralLoop.
Modify CavityResonator.is_CBI_stable to use  lcbi_growth_rate.
Update lcbi_growth_rate_mode, lcbi_growth_rate and lcbi_stability_diagram to optionally take  synchrotron_tune as input.

Add form factor option to set_optimal_detune.
Fix priniting in BeamLoadingEquilibrium.

interp_on_postion=False allows for faster tracking but the wake potential is interpolated on the bin center and each particle of the bin get the same value.

Update gitignore

Change the way Bunch particles coordinates are stored and accessed.
Speed-up TransverseMap.
Refactor WakePotential. 

Fix resonator wake function for negative time and update docstrings.

Synchrotron.to_pyat retrun a pyAT simple_ring element.

Fix to_pyat