You can now switch the document time on and off.

I realize that using the class attribute as an internal state is not my best
idea so far; this makes it way harder for anyone else to understand the style
sheet hierarchy.
Improved utils/simplify's handling of linear rings.

The previous approach failed for relatively large polygons that have small
holes in them: The 1st simplification results in a large error that allows
small holes to be collaped to stupid di-angles.
I enforced a minimum depth of 2 that gets me at least quadrangle every time.
Re-included the 1st simplification.

This looks much clearer now that polygon reduction produces useful polygons all
the time.
Changed the comment to reflect the new approach.
This is a better way of explaining it.