"Column view": Support confining interpolated fields to a desired length

[conner]

This introduces a simple modifier to field references specified in the format string:

Adding a suffix of the form [<integer>] will force the field value to be a string of that length. The field value, whether it's blank, shorter, or longer than the specified length will be of length <integer>. The consequence is a columnar output.

See commit message for a slightly longer explanation with a simple example.

I'm not entirely sure this fits a general desire and should be merged upstream, but it fits a need that my organization has, and we'll be using it : )