Make the compound schema a JSON definition

[shaded-enmity]

Currently only the common "generic" types like number, truth etc are handled using definitions.

To enable using the schemas in a context of tasks embedded into roles and playbooks we should make the main schema a definition as well that we can further reference from sub schemas.

[ssbarnea]

I didn't had time to check how Ansible schema looks but based on my brief experience with other schemas this is something I was expecting.

For example, the "block" element is allowed as a task but it can contain other tasks and nobody sane is expected to define what is acceptable as a task twice :)