Feature: Produce WARCS that match the 1.0 specification

[dcwalk]

The milestone for tracking this is here: https://github.com/datatogether/sentry/milestone/2

[b5]

quick update on this, turns out the 1.1 spec is still in the experimental phase, we're now targeting 1.0 spec, and progress on that is being made over at datatogether/warc, I'll change the title to match