Add the possiblity for using labels in combination with Histograms

[L7R7]

I'm currently trying to measure the latency of outgoing HTTP requests. I want to add a label for the path of the requested resource to allow grouping and filtering the latencies by path. As far as I can see, there's no way to do this with the current options.

I see that this question was discussed in the project this project was forked off, but I don't see a solution there. There's a workaround described in fimad#22 (comment), but I think it would be great to have the library made this use simpler to use.