Data-driven USets

@IainNZ 
As we discussed.  This is in usable, although not perfect, shape...  I have a whole list of "To Do's" beore it would be perfect.  

Please take a look.  I have some specific questions on 
- How should we handle the package dependencies? For example, I require Roots.jl  but, base JuMPeR does not...
- See my current edit to the main Jumper.jl.  Is this the best way to do this?
- How should we loop the test suite into the main JuMPeR test suite?  Right now run_tests.jl covers the DDUSets  package using FactCheck
- Can I maintain a separate wish-list of desired features for DDUsets via the issues section of github? Or will it be naturally mixed into the JuMPeR issues?

Thanks so much, brother. 

Vishal
Do you mean that .gitignore shoudln't be here, or the line referring to .pdf?