this allows us to serve a precise Content-Type header for all our pages, rendering treehouse usable in browsers that require one
(like terminal browsers---w3m, lynx)
this gives us a _much_ easier time with composing file systems, since you can call `query` on the inner file system and all the magic will be done for you
the overhead is technically slightly higher, but seems to be drowned out by other more expensive stuff; i couldn't measure a difference in my traces
this unfortunately means I had to cut some features (bye bye commit history! for now)
stuff's not quite 100% working just yet (like branch links, which were and are still broken)
we also don't have content_version impls just yet
