Update Audit Log format (and maybe file names)

[HEdingfield]

After doing a single big run (e.g. config_minneapolis_2013_scale.json), the audit log is too big for even Notepad++ to open (700 MB!). We need to figure out a better way to generate these; maybe splitting at 50 MB or some other more reasonable number. Recommend looking up limits for basic text editors and complying with the lowest one.