Refactoring, Code Style, Bugfixes

Some overall code refactoring, code style fixes and added more unit tests.

Bugfixes:

• #5

New Feature: ES6 fat arrow support

• Added support to register ES5 functions and ES6 fat arrow functions (thanks @calmdev! 🎉 ). Example:

// ES5
container.register('_', function() { 
  return require('lodash'); 
});

// ES6 fat arrow
container.register('_', () => require('lodash'));

• Added missing unit tests.
• Added missing asserts in unit tests.

1.2.7

• update (dev) dependencies
• update travis build tools