Reorient repository around "bundle preloading"

[littledan]

Following the discussion in IETF 110's WPACK WG meeting, there is a call for adoption of the "bundled responses" file format. This repository should be rearranged to focus on subresource loading, deferring the file format to the new WPACK repository once it is created.

I think it would be best if subresource loading initially focused on a simpler, imperative mechanism along the lines of this gist (which Shubhie from the Chrome team pointed out to me would be more accurately thought of as "prefetching" than preloading). Such a mechanism would form a flexible basis for the output of tools in the near-term, and a higher-level manifest-based mechanism as is currently described for subresource loading could be built on top of it.

With these changes, this repository might be more accurately called "WICG/~~batch-prefetching~~bundle-preloading".

[kinu]

(Naming bikeshed warning) Hi Dan, it's not super clear why "prefetching" is more accurate than preloading here to me, at least in a resource-hints terminology 'preload' means loading resources in advance for the same page, while 'prefetch' means loading resources for the next navigations. While if you're focusing more on the part that 'prefetch' usually loads resources into HTTP cache (while 'preload' may do a bit more) yes maybe, but with the reason I mentioned earlier (i.e. for the current page vs next pages) I doubt that renaming 'prefetch' is strictly better than 'preload'.