Fixed cookies + better "ready" handler + viewport masking + docs + misc other fixes...

* new cookie handler has proper support for setting expiry/path/domain/secure parameters + key/value encoding. The old one was not setting the cookie path, so even if you first came to http://goodcode.io/open-source/ and closed/agreed, you were again prompted when you went to the homepage (or any other page with a different path)
* new `contentLoaded()` helps testability and is more generic (works even when the script is injected after everything is already loaded / ready)
* optional covering of the viewport with a mask <div> (clicking on which is treated the same as the 'close/x' button) along with configurable opacity/background
* configurable z-index for the notice (incremented automatically by 1 if a cover is used so that it appears above the cover)
* fixed 'close/x' placement in markup so it looks better on small screens (since it's right-floated, it's better if it comes first in the markup)
* fixed the .cookiebanner className not being set
* shaved another kilobyte off the minified version