Dexy runs generated tests for selector examples.

We rename the example-verification target to
example-extraction, and make example-verification a target
that runs its own shell script.
Add support for setup code for example extractor.

This setup code is a code block marked with a .setup class.
Fix structure and matching in extracted tests.

Because of how HTML parsing works, we need to guarantee
a root node, so we wrap the input and output in a div. Then,
we include the div in the comparison we do after the fact.

We also compare rendered input to output ignoring
whitespace.
Run examples with color turned off.
Add setup code to CSS selector example docs.
Fix CSS selector example docs based on tests.

First errors caught by test failures during documentation
generation! :)
Ignore vim swap files.
Ignore tests generated by example extractor.