Added support for numbered lists

[raphtlw]

This fixes issue #18 and even supports nested list items.

In PR #35, I forgot to call the function that takes the blocks and adds the index for the bullet point. This is now fixed.

I solved this problem by introducing a new hook function that runs after each block's children is listed. I then "inject" a new property into the block object number, which just increments from 1 to max, and then in the rendering stage, use the property to render the numbered list bullets.

Result:

You can see it in production here

[souvikinator]

Awesome! Now it works. Thanks for the contribution. Should be live in the next release.