Add a mechanism to wait between data read

I discover your project which is almost what I would need but I wanted to add a feature to pause the content retrieval waiting for a given signal (like the withFinishDelayUntil mechanism).

This is very opened to feedback and maybe the implementation could be reworded or done differently.

What I basically was to test some code for a download manager so I needed to be able to abort the download and resume. I also add the support for range.