STY: pep8 fixes.
STY: More pep8 fixes.
First pass at making cumulative risk metrics match 1 year period.
Account for shifted columns in answer_key

Answer key had added so more columns for insight in to
the returns.
Update values since metrics have changed.
Use minute data for minute emission data.

Discovered when using [:dt] instead of .valid() to get
the current returns.
Create first day stats.
Handle first day return.
Use mean returns and treasury for sortino calculation.
Update indexes for answer key with Sortino.
Read downside risk.

Also fix sortino issues.
Use cumulative mean returns for comparison with dailies.

In downside risk.

Also hold on to the downside risk.
Update mapping into answer sheet.
Return 0.0 if there are no downsides.
Update answer key slots.
Use daily mean returns instead of cumulative.
Update risk answer key mapping.
Change degree of freedom.

Increase sig digits.
Update spreadsheet with rolling periods.
Make downside risk accept ddof for sample and population.