Add more tests and streaming interface

[aumetra]

No description provided.

[aumetra]

I literally can't get lol_html to produce any output on the last two failing tests.
This is so frustrating..

[aumetra]

This kinda fixes it but is really ugly.
In the beginning it does two linear scans across the string, one to count the openings tags, and one to count the closing tags.

Then it balances out the amount of opening and closing tags in the string, providing each open tag with a closing tag somewhere, then lol_html considers these as tags.

This is an ugly fix. I don't wanna merge that.

[aumetra]

Okay, this kinda fixes it. It still does two linear scans, but using the bytecount crate, and therefore SIMD accelerated primitives (when available).

And instead of allocating the entire content and appending them to the allocated chunk, we count the amount of unclosed opening tags and push them in using a for loop and the streaming interface of lol_html.

And since we were already using the streaming interface, this also adds a streaming interface to the sanitizer.

So.. closes #5