documentation needed for aperture_by_tracking output

[jeu8]

The aperture_by_tracking program has documentation in the fortran file, but this mostly focuses on the input. The output files do not have a description, but the columns are labeled fairly clearly in all of the output files except for pz_aperture_by_s.out. Based on the description of the program and file name it is not too hard to work out what they should be, although I get numbers that are much smaller than expected so I am unsure about the units being used.

None of the files have units listed, but this mainly causes a problem in pz_aperture_by_s.out

[DavidSagan]

@MichaelEhrlichman Can you take a look at this? Thanks.