Added the String.unroll_operator() and String.reduce_operator() extensions;

Example:
	say "tess"»-«"turs";        # prints: "es"
	say "Sdf"»+«"ie!";          # prints: "Sidef!"
	say "test"«|»;              # prints: "w"
	say "test"«++»;             # same as above ("w")