level_identifier should default to by ops
read single time slice method to pandas_reader
make histograms from a file.
Fail if fitter found a negative mass!
Implement find best fit. This is done if no times are input meaning
times are no longer required
default fit function should be periodic exponential
Check bootstrap bias.

If bootstrap average is different from the original then we have a
bias in the boot strapping! This means we don't have enough statistics
to get a valid fit.

This errors and quits, unless an unsafe flag is set