When multiple empty keys are found, make sure they are all stored in the output.

Even though most users won't run against this, in case multiple empty keys are
found, store them all under @? where ? is a 0-starting index.  Also include a
modified MATLAB file to test these conditions.  Note that MATLAB just ignores
all three inputs.
Add a .travis.yml file, to enable Travis CI.

Get this going for sanity checks.  Test against both JDK 6 and 7.