Version v0.3.0

• prop-types is now an external
• exported to window as ReactGoogleButton
• webpack updated to v2.6.0 (required changing webpack config)
• Styling improvements
  • drop shadow
  • button border radius
  • disabled style added (greyed out)
• Added disabled prop (with matching styling)
• Added type prop - 'light' or 'dark' for the different google styles (defaults to dark)
• Basic example actually uses built code
• Unit tests added that test rending of component with different props (label and disabled)