Quickreference doc of available playbook and task, conditional keywords

This is based on this idea discussed at https://groups.google.com/forum/#!topic/ansible-project/IVUwp9195Ek
It seems quiet necessary to have a comprehensive list and a table that compares between versions.

I think including a small usage description for each operator would also help, hence the links at the bottom.

Before I add more content, I'm looking for feedback on formatting and the comparison table.