Stream backtest logs to disk instead of holding in memory

[jaredbroad]

Expected Behavior

While backtesting stream logs to a temporary file instead of holding in memory to prevent memory issues.

Actual Behavior

Hold entire log in memory

Potential Solution

Adjust the backtest log handler.

Reproducing the Problem

Run a backtest with large volume of logging and monitor memory.

Checklist

• [x] I have completely filled out this template
• [x] I have confirmed that this issue exists on the current master branch
• [x] I have confirmed that this is not a duplicate issue by searching issues