HTML::Element: New dumping methods 'as_lol' and 'content_as_lol'.

I've always found it odd that there was a `new_from_lol` method, but no corresponding dumpers. Now I'm working on a project where such a dumping method might actually come in handy. Also, it allows DOM-based tests via `is_deeply`.

So I wrote one (well, two: `as_lol` and `content_as_lol`), and here it is, for your consideration. Naturally, I can change any part of the patch, be it code, idioms, indentation, or POD.

*Point of discussion*: I had originally wanted to offer an option to force an attribute hash ref, even if empty, but I can work around that in my project, so I didn't implement it. Would such an option still be useful?