Handling of descriptions

[britter]

Descriptions are now rendered into the the JavaDoc of getters.

Resolves #52, #53

[jjohannes]

Very good 👍

We should update the documentation about groups as well (add the description). This can be a follow up.

I tried this on a project and one thing I noticed, which is only indirectly related, is that if you navigate into the code to see the description, you also see all this implementation details clutter (like the injecting constructor). E.g.:

public abstract class Catalina {
    private final org.gradle.api.provider.Provider<String> home;
    @Inject
    public Catalina(ProviderFactory providers, ObjectFactory objects) {
        this.home = providers.gradleProperty("catalina.home").orElse(providers.environmentVariable("CATALINA_HOME"));
    }
    /**
     * Root of the Tomcat installation
     */
    public org.gradle.api.provider.Provider<String> getHome() {
        return this.home;
    }
}

We could consider generating interfaces for the extension and the group and work only with these in the type signatures. And then the JavaDoc would also go only there.