We want to precompile all js files with babel and for simplicity we
should keep all source files in the same folder.

The test are using `util` but I can't see any real problems with having
the tests importing a file inside the src folder

Precompiling all ES6 code to ES5 with babel to gain performance
Adding a .nodeignore file as well to ignore the source code and tests
files when publishing to npm

See commitizen#39

Added a npm-script for watching changes and re-compile the source file