Rename-Many: Add Transform parameter

[plastikfan]

This allows for a custom transform to be applied to the Pattern. The Transform param would be a script-block that takes a string representing the Pattern capture. This would be used for external commands that sit on top of Rename-Many, it would not be used interactively on the command line but could be if so desired.

The transform can only be be performed prior to invoking Post Processing to ensure that the post processing rules are still enforced and the Transform doesnt have to worry about breaking the post processing rukes.