Converts a string into a list of single-character strings.
DESCRIPTION
explode s returns the list of single-character strings that make up s, in
the order in which they appear in s. If s is the empty string, then an
empty list is returned.
FAILURE CONDITIONS
Never fails.
EXAMPLE
# explode "example";;
val it : string list = ["e"; "x"; "a"; "m"; "p"; "l"; "e"]