Change default behavior of CLI

This pull request changes default behavior of the command line tool.

* It will show usage if no argument is given, currently reads from stdin. Also add `--stdin` option.
* It will change default log level to INFO, currently WARN.
* It will add some tests.
Usage message is line wrapped. Fix [width](http://groovy.codehaus.org/gapi/groovy/util/CliBuilder.html#width).