An `re.sub` call always performs an evaluation of the first argument as a regular expression, even if no regular expression features were used. This has a significant performance cost and therefore should be used with care.
When `re.sub` is used, the first argument should be a real regular expression. If it's not the case, `str.replace` does exactly the same thing as `re.sub` without the performance drawback of the regex.
This rule raises an issue for each `re.sub` used with a simple string as first argument which doesn't contains special regex character or pattern.
