Use an Enum for the cursor styles which basically combines cursor shape
and blinking status.

This is in preparation for an upcoming patch to add support for DECRQSS
(Request Status String) escape sequences, which will use the cursor
styles in more than one location in the code.

Make sure the DECSCUSR escape sequences still work as before:
printf '\e[ q' #blinking block
printf '\e[0 q' # blinking block
printf '\e[1 q' # blinking block
printf '\e[2 q' # steady block
printf '\e[3 q' # blinking underscore
printf '\e[4 q' # steady underscore
printf '\e[5 q' # blinking ibeam/bar
printf '\e[6 q' # steady ibeam/bar

Executing reset in terminal will reset the cursor shape and blinking
settings to the current profile values.