New Require.js docs

I've done quite a bit of changes to the Require.js docs. I have created a running example at https://github.com/kjbekkelund/karma-requirejs which I have used as the basis for the description (I've also linked to it from the docs, so people can easily find a running setup — let me know if I should remove the link).

In the old docs Require.js `shims` weren't handled properly. Also, in this setup all includes are based on globs so you don't have to keep the config up to date when adding new files.

Let me know if the text needs more work. English is not my mother tongue so there might be some oddities, but hopefully it should be quite simple and understandable.