[Overlay] Rotate logfile instead of erasing every time

[TheButlah]

#187 Introduced a logfile. It will always erase the last log at program start. Since past errors are helpful when debugging users' errors, we should instead rotate the logfile. This means that there is some maximum file size (or number of lines) that we permit, and once we hit that maximum size, we truncate old logs until we are back at the maximum size.