New and Modified Commands

• Added descriptive text to the SDDS files for quantities in the sigma, centroid, and final output files.
• Increased the maximum length of the name for an element from 8 to 100 characters. This was requested by R. Bosch (SRC).
• The twiss_analysis command now creates quantities for the dispersion slope and alpha. Twiss analysis is no longer length-weighted, since this doesn't work when averaging over markers. Verbosity control was added to aid in confirming the elements included in the analysis.
• The track command now has a parameter (stop_tracking_particle_limit) that can be used to tell elegant to stop tracking when the number of particles falls below a preset limit.