Add support for custom value resolver

I want to implement a custom context in order to be able to resolve {{this.kind.of.value[0]}} my self.

Would it be possible to implement such a feature with:

interface Context {
     resolve(name: string): Promise<string>;
}


class DefaultContext implements Context {
    constructor(ctx: object) {
        this.ctx = ctx;
    }

    async resolve(name: string) {
        // ...
    }

}


class CustomtContext implements Context {
    // ...

    async resolve(name: string) {
        // ...
    }

}

and then passing the context (instance of custom context class) to the environnement or the renderer

I'll see if I can make a merge request for this