Update to use version 1.0.0 of rubyzip.

The API has been changed and the require files have moved so this is a backwards
incompatible change.
Update ReadMe with version 1.0 info.
Add a version badge to the ReadMe.
Update version info and changes file for release.
Add .ruby-version and .ruby-gemset files.
Split version information out into its own file.

So we can require it separately.
Use bundler and stop using jeweler.
Set up Travis CI.