Checks if a given word is an isogram or not. An isogram is a word that has no repeating letters.

• Convert string to lowercase/uppercase since capital letters do not equate to small letter.
• Iterate the string using 2 for loops using the iterators i and j. Where j starts of 1 more than i.
• If at any point str[i] is equal to str[j] return false.
• If the above does not happen till you reach the end of the string return true.