Calculator -- Time, GCD, LCM

Invalid date

1.add 'read me'
2.support number format

Last version as below,
1. (year, day, hour, minute, and second) can be calculated by the calculator.
2. Contains a simple standard calculator and add, subtract, multiply and divide units of time is a time calculator.
3. Change background color when you press three-dots option button in top-right corner.
4. Report supports divisors, prime, prime factorization, factors and multiples.
5. Factorial (n!) supports real number and negative number.