Collect challenging pages to test against

[waldyrious]

Ideally we'll want to setup CI to prevent changes from inadvertently breaking current functionality.

• http://users.rowan.edu/~polikar/WAVELETS/WTpart1.html: body bgcolor, body background (image), inline styles...
• http://www.hedonisticlearning.com/posts/category-theory-syntactically.html: dynamically created tags (<math>) that don't have style attributes.

If you know of heavily styled pages that could be used to stress-test unstyle, please mention them in a comment below!

[waldyrious]

See #18 for a list of pages that use tables for layout, which is another challenge for Downstyle.

[waldyrious]

For reference, a list of test pages to test the style of HTML elements (just exhaustive examples of HTML elements, defined straightforwardly, with no quirks) is listed at https://github.com/waldyrious/downstyler/issues/29#issuecomment-1763555889.