Include datadeps in API documentation

[m-fila]

The datadeps (spawn_datadeps, In, Out, etc.) have their own usage-page in the docs but weren't mention in the API documentation. The already provided docstrings can be used

I think it would be also useful to add a remark in the documentation that spawn_datadeps waits for all the tasks spawned. This part was unclear for me and I had to check the source code