VI compatibility:

Setting the size of the window does not work as expected.

Further extentions:

Add column mode delete/change/yank/put.
History stack for . command?

option verbose; when on keep the screen uptodate, when off only redisplay when
	input needed.
make linenr_t 32 bits, for editing more than 65000 lines.
remember message line for redraw.
use disk file when editing very large files