Option to mark warnings as errors

I'd love an option to mark error prone warnings as errors so that even warnings won't get ignored.

While it is possible to do the following:

``` groovy
tasks.withType(JavaCompile) {
options.compilerArgs += [ '-Werror' ]
}
```

it does not really suffice since all warnings are then marked as errors. Another option would be for every error prone rule to increase the severity though this will get impossible to maintain.

Maybe it could be something as simple as `-Xep:WarningsAsErrors`.