use DataDeps.jl for downloading

[oxinabox]

Hi @jbn,
this PR makes it so that the data is automatically downloaded.
See https://github.com/oxinabox/DataDeps.jl

Using it in WordNet.jl for this, is one of packages I had in mind when I was making DataDeps.
So if it is not going to be useful for this,
I would say that it is a problem with DataDeps.jl that need to be fixed (and a failure on my part -- I'ld appreciate the feedback).

This might need to wait for JuliaLang/METADATA.jl#13140
before it passes CI.

It also might want a CI test to check it can indeed construct one with no parameters, using the datadep.
That would involve setting the environment variable DATADEPS_ALWAYS_ACCEPT=true (to bypass the "Do you want to download?" screen.
Maybe even adding a cron test in travis to rerun periodically to check it the URL hasn't broken

[jbn]

This looks good to me. But, I'm in the make-or-break stage of my dissertation, so my review is cursory at best. @oxinabox you seem to be either the main or one of the main organizers for JuliaText. If you have pull rights, I think you're in a better position than I am to make these important decisions.

[oxinabox]

Fair enough,
I also am heading that way on my own PhD work, good luck.
I'll give it a second look-over myself, and merge.

[jbn]

(Just, FYI: @oxinabox. I should be wrapping up sometime in June / July. After which, I plan on writing some NLP-based tools, so I hope to start contributing again.)