Mocha testing framework

@imlucas 
1. Modified index.js to make it behave as a importable module
2. Created test/testUtil.js containing helper methods(setUp, tearDown, etc) that are used by different test cases
3. Wrote a template in empty.js that uses Mocha's testing logic (e.g. before, after, etc.)
4. Fixed a bug that prevents the program from exiting if size of data to generate is zero

If the structuring of the test looks good, I can write up more test cases :) 
Thanks!
Avoid moving the actual asserts of your tests into utils.  It hide's your actual api too much.  remember, tests are an amazing source of documentation.  For example http://visionmedia.github.io/superagent/docs/test.html