Adde DCREREADER_TWO_PAGE_THRESHOLD
Update credocument.lua
Added new functions to go to next/previous chapter that also work with 2-page layout
Use of new functions to jump to next/previous chapter that also works in 2-page mode
Merge pull request #729 from WS64/master

Added DCREREADER_TWO_PAGE_THRESHOLD and changed behaviour of next/previous chapter