Add test suite

Added a straight copy of the test suite from
[node.extend](https://npmjs.org/package/node.extend)
Ignore node_modules
Add tests to highlight config-extend's unique behavior

Added tests:
* demonstrating how arrays are merged differently from the
"standard" extend libraries.
* demonstrating the 'recursive-by-default' behavior
Add travis for CI tests
Merge pull request #2 from jasonkarns/tests

Add test suite