Feat: remove development code

[larvanitis]

Please, add the option to remove devel/debug code.

Use case: keep debugging code in source for development builds but remove it during production.

I am not sure how the implementation works but something in the lines of this would be great.

As attribute:

<div @dev-only>
  <!-- this element and its contents get removed -->
</div>

As comment:

<!-- @dev-only:start -->
...
<!-- everything here gets removed -->
...
<!-- @dev-only:end -->