[WIP] Trying to fix version issues.

So I've figured out that the issue can be fixed by changing the name of the `pymbar/pymbar` directory to `pymbar/PYMBAR`--and making the corresponding substitution in `setup.py`.  I don't think we actually want to make this name change, but I still haven't figured out another workaround.  

PS: I think the current Travis failure is related to #89