Fix lowercasing the key name by using the correct function.

For the records, it is clojure.string/lower-case.
Emulation works now for the first 24 terminal lines.
Let the terminal grow beyond the first 24 lines.

Provide a proper append-line method in the screens interface.
Get screen adjustment working which implements erase-in-display.

You'll see this feature in action by pressing CTRL-L in bash. All visible
lines are not simply discarded but pushed to the scrollback area.