Travis build and simple test 

As requested in #7:

Implementing a travis build, using conda.

Copied the framework from gaff2xml. If eventually we want to turn this into a conda package, the code base is available, but currently it is commented out.
To avoid confusion, maybe do a find-replace to change gaff2xml to host-guest?  My worry is that someone might eventually run a command like this and overwrite our gaff2xml build...