Added extensible converter

[hason]

Alternative to #103

[colinodell]

I do like this better than #103. Before I accept it, let me run a possible alternative by you:

What if we move CommonMarkConverter's current constructor to a static method, and then use the constructor you've provided here instead? So it would basically look like this:

class CommonMarkConverter
{
    public function __construct(DocParser $docParser, HtmlRendererInterface $htmlRenderer)
    {
        $this->docParser = $docParser;
        $this->htmlRenderer = $htmlRenderer;
    }

    public function convertToHtml($commonMark)
    {
        $documentAST = $this->docParser->parse($commonMark);

        return $this->htmlRenderer->renderBlock($documentAST);
    }

    public static function create(array $config = array())
    {
        $environment = Environment::createCommonMarkEnvironment();
        $environment->mergeConfig($config);

        $docParser = new DocParser($environment);
        $htmlRenderer = new HtmlRenderer($environment);

        return new static($docParser, $htmlRenderer);
    }
}

The downside is that it'll break BC. Technically that's okay with 0.x releases, but I've always intended this class to remain consistent while allowing the internals to change drastically.

The upside is that CommonMarkConverter will be injectable like it should be.

I'm not sure how I feel about the static method though.

Any thoughts on this? (If you like this approach, should the create() method be called something better?)

/cc @philsturgeon and @GrahamCampbell - I'd greatly appreciate any guidance you might have on this.

[colinodell]

I think I've decided on the direction I'd like to go (for now anyway):

1. Create a new class called Converter or BaseConverter.
2. Make its constructor accept a DocParser and HtmlRendererInterface
3. Move the convertToHtml method into it
4. Have CommonMarkConverter extend from this class
5. Have CommonMarkConverter's constructor create the Environment, DocParser, and HtmlRenderer, passing the latter two into the parent's constructor.

This ensures backwards-compatibility and adds the functionality you're looking for in a logical manner. It's similar to your proposed change, but with the inheritance hierarchy reversed.

@hason if you're up to making that change I will gladly accept it :) Otherwise I'll work on it sometime this week.

[hason]

@colinodell Accepted and updated.

[colinodell]

Awesome, thanks @hason!