Adapt ArviZ docstrings about arviz.jl HOT 1 CLOSED

I figured out how to have two types of docs in 2 contexts. For every function forwarded without modification to arviz, we define two types of documentation. The documentation that appears in the docs will just consist of the link to the same function in ArviZ's docs. To make the help messages in the REPL useful, we'll make them show the ArviZ docs.

We'll only define non-linking docs for functions that have been modified in some way. Thus the ArviZ.jl docs will also serve as a diff between the two packages. Then there's no need to adapt ArviZ's docstrings except for those cases where we changed something.

from arviz.jl.