Windows support

The new `@cloudflare/doca` probably doesn't work any better on Windows than the old.

* `require` paths in schema.js use forward slashes
* when generating form data file upload curl examples, the syntax is different on Windows
* commands in `build` and `build:nojs`are not Windows-friendly, per @wiggisser in @cloudflare/doca#25:

You must set an environment variable by set SOMEVAR=value. Further more this is a separete command so you'll have to add an additional && before the call to webpack like for instance
```
"cleanwin": "rmdir /S /Q build",
"buildwin": "npm run cleanwin && set NODE_ENV=production && webpack --config webpack/config.prod.withjs.babel.js && del build\\static-*",
"buildwin:nojs": "npm run cleanwin set && NODE_ENV=production && webpack --config webpack/config.prod.nojs.babel.js && del build\\static-* && del build\\app-*.js"
```
From @aphilaja in cloudflare/doca#26:

I don't think Windows build has to be a special case:

use rimraf module instead of del and rm -rf.
use webpack -p instead of NODE_ENV=production
Then it should works equally in win & *nix.

Edit: Hmm.. not sure if -p sets NODE_ENV to production. If that's not the case and the env var is needed, I think there is Webpack plugin for it.