swift3の文字列操作（String.substring）メモ ref: http://qiita.com/MTattin/items/bf32562cd7d03c49026f

file0.swift

        let Str: String = "123456789"
        ///
        /// 先頭１文字 - 1
        ///
        print("\(Str.substring(to: Str.index(after: Str.startIndex)))")
        ///
        /// 先頭１文字以外 - 23456789
        ///
        print("\(Str.substring(from: Str.index(after: Str.startIndex)))")
        ///
        /// 末尾１文字 - 9
        ///
        print("\(Str.substring(from: Str.index(before: Str.endIndex)))")
        ///
        /// 末尾１文字以外 - 12345678
        ///
        print("\(Str.substring(to: Str.index(before: Str.endIndex)))")
        ///
        /// 先頭から？文字 - 12345
        ///
        print("\(Str.substring(to: Str.index(Str.startIndex, offsetBy: 5)))")
        ///
        /// 末尾から？文字 - 56789
        ///
        print("\(Str.substring(from: Str.index(Str.endIndex, offsetBy: -5)))")
        ///
        /// 先頭？文字以外 - 6789
        ///
        print("\(Str.substring(from: Str.index(Str.startIndex, offsetBy: 5)))")
        ///
        /// 末尾？文字以外 - 1234
        ///
        print("\(Str.substring(to: Str.index(Str.endIndex, offsetBy: -5)))")
        ///
        /// ？から？文字 - 456
        ///
        print("\(Str.substring(with: Str.index(Str.startIndex, offsetBy: 3)..<Str.index(Str.endIndex, offsetBy: -3)))")