More problem solutions

- Problem 4: Largest palindrome product
- Problem 5: Smallest multiple
- Problem 6: Sum square difference
- Problem 7: 10001st prime
- Problem 10: Summation of primes
- Problem 16: Power digit sum
- Problem 50: Consecutive prime sum

I’ve solved the above problems using Xtend. Solutions are relatively easy but my code is far from optimized. For example, my solution for Problem 50 took about 950 seconds and others solve it less than a millisecond ðŸ™‚