fix: remove hard-coded paths to SlimerJS, make it work on Windows; fix options handling

This bug fix

- declares the SlimerJS module explicitly as a dependency
- removes hard-coded paths for all platforms
- creates a working setup on Windows, runs SlimerJS without relying on slimerjs.bat
- properly processes options and config
- cleans up the code, structuring it like the PhantomJS launcher.

The Windows part of the fix was originally proposed by @bessdsv. Thank you!
Merge pull request #10 from hashchange/master

fix: remove hard-coded paths to SlimerJS, make it work on Windows; fix options handling