Added documentation for replace in next function

[ronald-d-rogers]

I was stuck on this one for a while because it was not in the documentation and want to add it for the benefit of others.

[posva]

Thanks for reporting this. It's not quite the doc that should be added because the point is that the argument of the next function is a RawLocation. But the doc doesn't says make it clear about the types

[ronald-d-rogers]

Yes you're probably right. I'm definitely not equal to the task of documenting RawLocation at the moment though. Perhaps an issue should be created instead.