generalized paths across OS and root directories

Hi Stephanie,

Great work!  This PR is what I had to do to be able to start running the code on my machine.  It does two new things:

 - No more hard-coded paths - I get the current working directory from `os.getcwd()`.  This does however expect that the program was launched from the root directory of the project.

 - In microsoft's infinite wisdom, they apparently use the reverse \ for delimiting directories WRT unix.  I use `os.name == "nt"` to decide if I'm on a windows machine, whereupon I use their delimiter, or else just / everywhere else.  I don't actually have a windows box, so please check if this actually works there!

You can certainly solve these problems better than a giant Python noob like me, so this may just be an interim hack until you have time to look at it yourself - but it lets us both (I hope) run the code for now.  Let me know!