Check if character is vowel

        /// <summary>
        /// Checks if ch is vowel or in [AEIOUaeiou].
        /// </summary>
        /// <param name="ch"></param>
        /// <returns></returns>
        public static bool IsVowel(char ch)
        {
            // Not in range.
            if (ch < 'a' || ch > 'U') return false;
            if (ch > 'U') // 0x55
            {
                return ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u';
            }
            return ch == 'A' || ch == 'E' || ch == 'I' || ch == 'O' || ch == 'U';
        }