Initial commit
Add support for Crosswalk Java Extensions

By passing --extensions path/to/extensions we can now include a custom
extension to the project that will expose a JavaScript API that will
talk to a custom Java backend.
Add option for adding extra Java libraries to the project

Use --extra-libraries path/to/directory/with/jar to include new
.jar files to the project. All .jar files on the directory will
be added.
Make sure the path exists before using

Instead of fuzzy error messages, tell the user what is going on.
Bump version