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.
There are some inconsistencies between openpyxl  < 2.0 and versions >= 2.0, but this is currently taken care of in the script itself. If I wanted to include version requirements, what would be the syntax for that?