Upgrade

Hey @gillesruppert I've done some improvements, some of them are important and some are just up to what I assumed is better, which of course might feel opinionated.

If it's too harsh or too breaking from your point of view, let me know.

What I've changed:
- Middleware signature is `(config/*, options*/)` where config at all times must be _url:path_ hash map. I removed support for two strings.
- Middleware accepts _options_ that can be passed to webmake. By default `cache: true` is set, as in 99.99% cases it's what you want to do. Other options must be set explicitly (I did not set `sourcemap: true` as it's not always desirable)
- Match url's with _pathname_ token, so e.g. query strings do not interfere _(parsing url may not feel right from performance point of view, but it's strictly dev setup, nobody would want to run this middleware on production, so I take that's totally fine)_
- Improve error reporting
- Lint, style improvements (use strict, and minor whitespace adjustments)
- Update package.json, refresh dependencies, bump version