Predicate modifier to strip colors and friends?

[epage]

Like the modifier to normalize newlines, it could help assert_cmd users to offer a way to strip things like ansi color codes.

While assert_cmd more focus on CLI that only use stdout/stderr (including sanitize the output a.k.a removing terminal code for color, blinking text, empty line, and others)

From @DrSensor at assert-rs/assert_cmd#74