Sapper uses URLs in the same namespace as the app

[tv42]

I noticed this with export, but it holds for running the sapper server component too.

Sapper 0.27.16 uses URLs in the /client/ path for its own purposes. This sounds a bit too generic for the framework to steal, a webapp should be free to use /client/[id]/blah etc for it's own purposes.

Creating a src/routes/client.svelte does not break sapper's internal use, and the filenames sapper puts there aren't likely to collide, but it's still arguably ugly, confusing, a bad design, and who knows whether things will collide in the future or not. Namespaces just simply should not be mushed together like this.

Other things in __sapper__/export, that aren't controlled by static/ or src/routes/, are service-worker.js and service-worker-index.html.

I'd argue all sapper-specific URLs should be constrained to something like /_sapper/*.

[benmccann]

Most of the pain was addressed by #1307. We could probably make it configurable or do more, but hopefully it solves the issues that most users ran into