Filled box shouldn't use border or border radius at page breaks

[mojavelinux]

When a filled box spans more than one page, the border and border radius should be dropped at the page breaks.

This is a follow-up from issue #11.

[mojavelinux]

I've implemented a different approach for literal / listing blocks that uses dashed lines at the boundaries of pages.

[mojavelinux]

This has been implemented for literal / listing block and sidebar blocks (#259). It hasn't yet been implemented for example blocks, but that depends on #362 (which is where it should be addressed).