improve dependency fetcher with clearer parameters

[mmcky]

@oyamad Once this is merged -- unfortunately this will break the notebook. But I think you guys are right -- this will be clearer to use.

@cc7768 Is this what you mean re issue #278?

[coveralls]

Coverage remained the same at 82.503% when pulling 4a358bc on update-nb-fetcher into 75e12dc on master.

[coveralls]

Coverage remained the same at 82.503% when pulling b4dc277 on update-nb-fetcher into 75e12dc on master.

[cc7768]

Yes, this is roughly what I had in mind. I think the dictionary behavior for files was a bit confusing because the folder name could be specified in two different places (either as the key in the dictionary or as the deps argument).

It would be nice if we could have someone write a short example of fetching files from each of the different repositories and include it in the documentation for this function to make it easier for others to put this function to work.

[mmcky]

Before I merge this I really should write a test.

[coveralls]

Coverage increased (+0.4%) to 82.857% when pulling c5c90c1 on update-nb-fetcher into 75e12dc on master.