Add moveParagraphForwardAndModifySelection: and moveParagraphBackwardAndModifySelection:
In all after changing selection, make sure to scroll the selection into view
Fix a bug where moving down from a selection that includes the end of a line fragment caused the caret to be incorrectly drawn two lines down instead of one.
Fix a bug where adding a newline inside a non-first line fragment in a line would cause the caret to incorrectly go to the beginning of the current fragment rather than the beginning of the new one.
Fix a bug where performing the following actions would cause a crash do to invalid line cache contents
Add a newline at the beginning of a wrapped line fragment
moveParagraphForwardAndModifySelection:
andmoveParagraphBackwardAndModifySelection: