Number of Palindromic Substrings
Recursive soln:
1. Here base condition comes out to be i>j if we hit this condition, return 1.
2. We check for each and every i and j, if the characters are equal,
if that is not the case, return 0.
3. Call the is_palindrome function again with incremented i and decremented j.
4. Check this for all values of i and j by applying 2 for loops.