make TemplateEngine configurable (see #211)

[decebals]

A proof of concept. See #211 for more information.

Conclusion:

• Groovy, we export MarkupTemplateEngine but my feeling is that we cannot modify some configuration parameters using this object
• Jade, we export JadeConfiguration, not the engine
• Pebble, we export PebbleEngine, perfect
• Trimou, we export MustacheEngine but all settings are done in a previous step in MustacheEngineBuilder, my feeling is that we cannot modify some configuration parameters using this object (MustacheEngine)
• Freemarker, we export Configuration, not the engine
• Velocity, we export Velocity engine but all settings are done in a previous step

So, I don't have a perfect fit. I will try to dig more. Any idea is welcome.

[gitblit]

A perfect fit looks to be difficult.

Maybe a better alternative would be to make it easier to subclass a TemplateEngine and then manually assign it rather than trying to tweak whatever is discovered?

public class TrimouTemplateEngine {
    @Override
    public void init(Applicaiton application) {
        // normal init stuff...

        // allow custom initialization
        init(builder);

        // create final engine
        engine = builder.build();
    }

    protected void init(MustacheEngineBuilder builder) {
    }
}

public class MyMoustache extends TrimouTemplateEngine {
    @Override
    protected void init(MustacheEngineBuilder builder) {
        builder.registerHelper("trimmer", new MyMoustacheTrimmer());
    }
}

With this we would do:

Application.get().setTemplateEngine(new MyMoustacheEngine());

[decebals]

Good idea. I will try your approach.