Shim out fs access

[cblgh]

we recently had a pr that added a much-welcomed settings file (#89) however, as @khubo recently realized, this is fudging up cabal when used in the browser!

so we need to extract the settings logic into something that can work in the browser. so rather operate on the path using something that relies on the random-access-* ecosystem (like we're already doing in src/storage-node.js / src/storage-browser.js)