Create a GitHub Pages website for jetzt

This PR creates a simple static GitHub Pages website for jetzt.

It includes information from the project's README.md, formatted in a more site-friendly way, plus a usable bookmarklet link. (This can be updated to the more recent version, once it is finalised.)

The site should look like this:

![screen shot 2014-03-20 at 20 11 07](https://f.cloud.github.com/assets/23469/2477032/06a2e146-b06c-11e3-8410-4b0ce0420661.png)

This design is intended to be a reasonable basis for further work, but may require some tweaking.

I have created a favicon.ico which I think is better than the current extension icon. If you agree, I can produce extension icons to match.

This PR is intended to close issues #77 and #56.