Windows compatibility and CommonJS interop change back to Babel 5 functionality

[khell]

Hi, I have two changes.

Windows Compatibility
Use rimraf package which mirrors rm -rf behaviour. This is for compatibility with Windows on the
clean script.

CommonJS interop issue with exports.default
Because you're using Babel 6, exports default gets transformed to exports.default as ES6 module. For CommonJS interoperability it is needed to now import this module with .default which is not desirable as evident by #116. babel-plugin-add-module-exports reverts to Babel 5 functionality, which does the same as above, but also adds a module.exports line for CommonJS.

[stipsan]

Thanks @khell! 😄