Problems with `fetch_nb_dependency`

[cc7768]

@thomassargent30 was trying to download files from QuantEcon.applications and the current dependency fetcher doesn't seem to be able to do this easily.

It might be useful to do the following two things:

• Currently, the function takes a deps argument because it helps you get to the dependency folder of QuantEcon.Notebooks. In line 73 of the function it joins the repo, raw, deps, and other arguments together. It might make sense to remove the deps argument altogether (or rename it to be folder) and just require people to use the dictionary approach when getting files from QuantEcon.Applications... There could be a few other possible solutions to this, but I think the current design prevents the code from being able to fetch files from other repositories (which I think was one of the goals).
• Write some examples of how this function works.

Both of these seem like relatively easy tasks? Do we have any newer members of the team that might be capable of doing this?

Maybe @mmcky has some design thoughts to fix this?

[oyamad]

I agree deps will better be folder, or directory.

A use case is found in Cell [44] in here.

[mmcky]

Only thing left is to:

• Write some examples of how this function works.

[mmcky]

Closing based on PR #279 and #320