Feature: Add backpressure support and support throttling for streaming outgoing chunked request body. (#148 by @clue)

Feature: Start sending outgoing request even when streaming body doesn't emit any data yet. (#150 by @clue)

Feature: Only start request timeout timer after streaming request body has been sent (exclude upload time). (#151 and #152 by @clue)

Feature: Reject request when streaming request body emits error or closes unexpectedly. (#153 by @clue)

Improve download benchmarking script and add new upload benchmark. (#149 by @clue)