Exclude development stuff from repository autogenerated ZIP archives
People that install this library via composer don't need the test/sample/doc stuff, they just need the library itself.
This PR removes the development directories and files from the repository auto-generated ZIP archives.
Since these development files/directories will still be available via `git clone`, Travis is happy, developers are happy, and so are end-users (they won't have unneeded stuff in production machines).
Michele Locati