could I merge in socket OutputProgressEvent support?

[rblaa]

Thank you for making this wonderfully cleanly coded library. It lets us all have the full control we need to talk to servers in the way we want.

I have implemented support for OutputProgressEvent events on socket writes. This allowed me to finally upload large photos efficiently.

I would like to submit my modest changes to the main branch. Are you interested? If so, what is the best way of doing that?