Implement a nicer status range check

[laurentsenta]

@hacdias implemented StatusBetween(500, 599), it's easy to implement and does the job 👍

For the sake of readability & user-friendliness, we could implement a nicer matcher like .Status("5xx").

see #157 (comment)

[guillaumemichel]

Triage notes:

• StatusBetween(500, 599) should be good enough
• It is better to be explicit rather than checking for "5xx"