Stringで[1..4]とかできるようにするextension

gistfile1.swift

extension String {
    subscript(range:Range<Int>) -> String {
        return self[advance(self.startIndex, range.startIndex)..advance(self.startIndex, range.endIndex)]
    }
}

var s = "abcdefghij"
s[1..4] // print "bcd"
s[1...4] // print "bcde"