display available {data,metrics,benchmarks,models} in documentation

[mschrimpf]

our API reference currently displays that there exist pools of plugins, but there is nothing on what the individual plugins actually are, nor does it display any documentation inside the plugins themselves.

Is there a way to automatically display the dictionary contents, and even better link it to the respective plugin reference?

[kvfairchild]

(Note for future self): https://sphinxcontrib-bibtex.readthedocs.io/en/latest/

[kvfairchild]

Handled in (draft) #232