#11 cursor in line past last line

[Oswald Buddenhagen]

the cursor should be able to enter the line past the last
line, i.e., treat the EOL as a character past which one
can append text.

making it consistent with column behavior would mean
allowing the cursor to enter arbitrary lines past EOF, but
that's generally pointless, and dragging consistency
further, an option "keep trailing lines" would be
necessary.