Fix step failure

I forked your step and created a small app that used it. This app was failing on the `rm` command that tried to remove a non existing file from the cache. I added a `-f` option to the command to prevent it returning an failing exit code.

Next to that I also removed the `set -x` and added functional logging. I also added a `README.md` so the step looks nicely in the wercker directory.

The pull request bumps the version from `0.0.3` to `0.0.4`.