Add Unique Mode

[wdahlenburg]

Unique Mode was added to qsreplace to allow modifying the value of parameters one at a time, rather than updating all values at once.

This is useful in scenarios where validation is applied to some parameters, but not all. Injecting a payload iteratively into each parameter value allows for finer control on bypassing validations and troubleshooting which parameters are subject to injection attacks. The trade-off is path explosion for requests with a large number of parameters.

The readme was updated to include a sample usage. The unique mode works in combination with append mode if both flags are set.

[manasmbellani]

Excellent update @wdahlenburg, really like it. Thank you. Haven't tried this out yet, but can't wait to give it a try. =)