Added --unittest option and decimal print test.

No longer runs unit tests at startup by default, for faster startup.
Added unit test for correct width of print for decimal numbers.
It logs a loud warning message if a floating-point number is found that causes the column widths to print different from what they are expected to be.
The unit test fails because it catches the existing bug in the formatting, but if my "rounding" pull request is applied, then it passes (makes no output).