Added `--chapter-mark` configuration

Signed-off-by: Or'el Ben-Ya'ir <orelbenyair@gmail.com>
Moved "chapterMark" to global ebook config

Signed-off-by: Or'el Ben-Ya'ir <orelbenyair@gmail.com>
Added `pageBreaksBefore` config option

Signed-off-by: Or'el Ben-Ya'ir <orelbenyair@gmail.com>
Fixed variable misspelling in ebook config

Signed-off-by: Or'el Ben-Ya'ir <orelbenyair@gmail.com>